diff --git content/browser/appcache/appcache_internals_ui.cc content/browser/appcache/appcache_internals_ui.cc
index d95dcaf34949..5794a5fdf506 100644
--- content/browser/appcache/appcache_internals_ui.cc
+++ content/browser/appcache/appcache_internals_ui.cc
@@ -375,8 +375,8 @@ void AppCacheInternalsUI::CreateProxyForPartition(
     StoragePartition* storage_partition) {
   scoped_refptr<Proxy> proxy =
       new Proxy(weak_ptr_factory_.GetWeakPtr(), storage_partition->GetPath());
-  proxy->Initialize(static_cast<StoragePartitionImpl*>(storage_partition)
-                        ->GetAppCacheService());
+  proxy->Initialize(static_cast<ChromeAppCacheService*>(
+      storage_partition->GetAppCacheService()));
   appcache_proxies_.push_back(proxy);
 }
 
diff --git content/browser/background_fetch/background_fetch_service_impl.cc content/browser/background_fetch/background_fetch_service_impl.cc
index f116ff5aad35..73544f3181d6 100644
--- content/browser/background_fetch/background_fetch_service_impl.cc
+++ content/browser/background_fetch/background_fetch_service_impl.cc
@@ -42,8 +42,7 @@ void BackgroundFetchServiceImpl::CreateForWorker(
       BrowserThread::IO, FROM_HERE,
       base::BindOnce(
           BackgroundFetchServiceImpl::CreateOnIoThread,
-          WrapRefCounted(static_cast<StoragePartitionImpl*>(
-                             render_process_host->GetStoragePartition())
+          WrapRefCounted(render_process_host->GetStoragePartition()
                              ->GetBackgroundFetchContext()),
           origin, nullptr /* render_frame_host */, std::move(request)));
 }
@@ -64,8 +63,7 @@ void BackgroundFetchServiceImpl::CreateForFrame(
       BrowserThread::IO, FROM_HERE,
       base::BindOnce(
           BackgroundFetchServiceImpl::CreateOnIoThread,
-          WrapRefCounted(static_cast<StoragePartitionImpl*>(
-                             render_process_host->GetStoragePartition())
+          WrapRefCounted(render_process_host->GetStoragePartition()
                              ->GetBackgroundFetchContext()),
           render_frame_host->GetLastCommittedOrigin(), render_frame_host,
           std::move(request)));
diff --git content/browser/blob_storage/chrome_blob_storage_context.cc content/browser/blob_storage/chrome_blob_storage_context.cc
index 203e9c7e94a9..b4260e27ae6a 100644
--- content/browser/blob_storage/chrome_blob_storage_context.cc
+++ content/browser/blob_storage/chrome_blob_storage_context.cc
@@ -87,6 +87,11 @@ class BlobHandleImpl : public BlobHandle {
 
 ChromeBlobStorageContext::ChromeBlobStorageContext() {}
 
+// static
+const void* ChromeBlobStorageContext::GetUserDataKey() {
+  return kBlobStorageContextKeyName;
+}
+
 ChromeBlobStorageContext* ChromeBlobStorageContext::GetFor(
     BrowserContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
diff --git content/browser/blob_storage/chrome_blob_storage_context.h content/browser/blob_storage/chrome_blob_storage_context.h
index 26cf1ebfdffc..f6de541d25d1 100644
--- content/browser/blob_storage/chrome_blob_storage_context.h
+++ content/browser/blob_storage/chrome_blob_storage_context.h
@@ -50,6 +50,8 @@ class CONTENT_EXPORT ChromeBlobStorageContext
  public:
   ChromeBlobStorageContext();
 
+  static const void* GetUserDataKey();
+
   // Must be called on the UI thread.
   static ChromeBlobStorageContext* GetFor(
       BrowserContext* browser_context);
diff --git content/browser/bluetooth/web_bluetooth_service_impl.cc content/browser/bluetooth/web_bluetooth_service_impl.cc
index f061eca7c86b..0fc07c9c4eb8 100644
--- content/browser/bluetooth/web_bluetooth_service_impl.cc
+++ content/browser/bluetooth/web_bluetooth_service_impl.cc
@@ -1233,9 +1233,9 @@ url::Origin WebBluetoothServiceImpl::GetOrigin() {
 }
 
 BluetoothAllowedDevices& WebBluetoothServiceImpl::allowed_devices() {
-  StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
+  StoragePartition* partition =
       BrowserContext::GetDefaultStoragePartition(
-          web_contents()->GetBrowserContext()));
+          web_contents()->GetBrowserContext());
   scoped_refptr<BluetoothAllowedDevicesMap> allowed_devices_map =
       partition->GetBluetoothAllowedDevicesMap();
   return allowed_devices_map->GetOrCreateAllowedDevices(GetOrigin());
diff --git content/browser/browser_context.cc content/browser/browser_context.cc
index 840cafc185f4..aa16726a33ce 100644
--- content/browser/browser_context.cc
+++ content/browser/browser_context.cc
@@ -151,11 +151,18 @@ StoragePartition* GetStoragePartitionFromConfig(
   StoragePartitionImplMap* partition_map =
       GetStoragePartitionMap(browser_context);
 
-  if (browser_context->IsOffTheRecord())
+  if (browser_context->IsOffTheRecord() || browser_context->GetPath().empty())
     in_memory = true;
 
-  return partition_map->Get(partition_domain, partition_name, in_memory,
-                            can_create);
+  StoragePartitionImpl* partition_impl =
+      partition_map->Get(partition_domain, partition_name, in_memory,
+                         can_create);
+  if (partition_impl->browser_context() == browser_context)
+    return partition_impl;
+
+  // |browser_context| is a CefBrowserContextProxy object.
+  return partition_impl->browser_context()->
+      GetStoragePartitionProxy(browser_context, partition_impl);
 }
 
 void SaveSessionStateOnIOThread(
@@ -629,6 +636,11 @@ ServiceManagerConnection* BrowserContext::GetServiceManagerConnectionFor(
 BrowserContext::BrowserContext()
     : unique_id_(base::UnguessableToken::Create().ToString()) {}
 
+// static
+const void* BrowserContext::GetStoragePartitionMapUserDataKey() {
+  return kStoragePartitionMapKeyName;
+}
+
 BrowserContext::~BrowserContext() {
   CHECK(GetUserData(kMojoWasInitialized))
       << "Attempting to destroy a BrowserContext that never called "
diff --git content/browser/devtools/protocol/network_handler.cc content/browser/devtools/protocol/network_handler.cc
index 905fe910bebb..abf75841dd86 100644
--- content/browser/devtools/protocol/network_handler.cc
+++ content/browser/devtools/protocol/network_handler.cc
@@ -927,8 +927,7 @@ class BackgroundSyncRestorer {
     scoped_refptr<ServiceWorkerDevToolsAgentHost> service_worker_host =
         static_cast<ServiceWorkerDevToolsAgentHost*>(host.get());
     scoped_refptr<BackgroundSyncContext> sync_context =
-        static_cast<StoragePartitionImpl*>(storage_partition_)
-            ->GetBackgroundSyncContext();
+        storage_partition_->GetBackgroundSyncContext();
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,
         base::BindOnce(
diff --git content/browser/devtools/protocol/service_worker_handler.cc content/browser/devtools/protocol/service_worker_handler.cc
index 06c7cf436fd7..1f6e5182191f 100644
--- content/browser/devtools/protocol/service_worker_handler.cc
+++ content/browser/devtools/protocol/service_worker_handler.cc
@@ -170,8 +170,7 @@ void ServiceWorkerHandler::SetRenderer(int process_host_id,
     return;
   }
 
-  storage_partition_ =
-      static_cast<StoragePartitionImpl*>(process_host->GetStoragePartition());
+  storage_partition_ = process_host->GetStoragePartition();
   DCHECK(storage_partition_);
   context_ = static_cast<ServiceWorkerContextWrapper*>(
       storage_partition_->GetServiceWorkerContext());
diff --git content/browser/devtools/protocol/service_worker_handler.h content/browser/devtools/protocol/service_worker_handler.h
index ec9ab86d0ca6..0fe5219f1e84 100644
--- content/browser/devtools/protocol/service_worker_handler.h
+++ content/browser/devtools/protocol/service_worker_handler.h
@@ -24,7 +24,7 @@ class BrowserContext;
 class RenderFrameHostImpl;
 class ServiceWorkerContextWatcher;
 class ServiceWorkerContextWrapper;
-class StoragePartitionImpl;
+class StoragePartition;
 
 namespace protocol {
 
@@ -74,7 +74,7 @@ class ServiceWorkerHandler : public DevToolsDomainHandler,
   bool enabled_;
   scoped_refptr<ServiceWorkerContextWatcher> context_watcher_;
   BrowserContext* browser_context_;
-  StoragePartitionImpl* storage_partition_;
+  StoragePartition* storage_partition_;
 
   base::WeakPtrFactory<ServiceWorkerHandler> weak_factory_;
 
diff --git content/browser/download/download_manager_impl.cc content/browser/download/download_manager_impl.cc
index 37cabf2c9ffa..a5165fdbfdf6 100644
--- content/browser/download/download_manager_impl.cc
+++ content/browser/download/download_manager_impl.cc
@@ -87,9 +87,9 @@
 namespace content {
 namespace {
 
-StoragePartitionImpl* GetStoragePartition(BrowserContext* context,
-                                          int render_process_id,
-                                          int render_frame_id) {
+StoragePartition* GetStoragePartition(BrowserContext* context,
+                                      int render_process_id,
+                                      int render_frame_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   SiteInstance* site_instance = nullptr;
@@ -99,8 +99,7 @@ StoragePartitionImpl* GetStoragePartition(BrowserContext* context,
     if (render_frame_host_)
       site_instance = render_frame_host_->GetSiteInstance();
   }
-  return static_cast<StoragePartitionImpl*>(
-      BrowserContext::GetStoragePartition(context, site_instance));
+  return BrowserContext::GetStoragePartition(context, site_instance);
 }
 
 bool CanRequestURLFromRenderer(int render_process_id, GURL url) {
@@ -266,7 +265,7 @@ base::FilePath GetTemporaryDownloadDirectory() {
 #endif
 
 scoped_refptr<download::DownloadURLLoaderFactoryGetter>
-CreateDownloadURLLoaderFactoryGetter(StoragePartitionImpl* storage_partition,
+CreateDownloadURLLoaderFactoryGetter(StoragePartition* storage_partition,
                                      RenderFrameHost* rfh,
                                      bool is_download) {
   network::mojom::URLLoaderFactoryPtrInfo proxy_factory_ptr_info;
@@ -283,7 +282,7 @@ CreateDownloadURLLoaderFactoryGetter(StoragePartitionImpl* storage_partition,
     }
   }
   return base::MakeRefCounted<NetworkDownloadURLLoaderFactoryGetter>(
-      storage_partition->url_loader_factory_getter(),
+      base::WrapRefCounted(storage_partition->url_loader_factory_getter()),
       std::move(proxy_factory_ptr_info), std::move(proxy_factory_request));
 }
 
@@ -1127,7 +1126,7 @@ void DownloadManagerImpl::InterceptNavigationOnChecksComplete(
       tab_referrer_url = entry->GetReferrer().url;
     }
   }
-  StoragePartitionImpl* storage_partition =
+  StoragePartition* storage_partition =
       GetStoragePartition(browser_context_, render_process_id, render_frame_id);
   in_progress_manager_->InterceptDownloadFromNavigation(
       std::move(resource_request), render_process_id, render_frame_id, site_url,
@@ -1177,10 +1176,8 @@ void DownloadManagerImpl::BeginResourceDownloadOnChecksComplete(
         base::MakeRefCounted<WebUIDownloadURLLoaderFactoryGetter>(
             rfh, params->url());
   } else if (rfh && params->url().SchemeIsFileSystem()) {
-    StoragePartitionImpl* storage_partition =
-        static_cast<StoragePartitionImpl*>(
-            BrowserContext::GetStoragePartitionForSite(browser_context_,
-                                                       site_url));
+    StoragePartition* storage_partition =
+        BrowserContext::GetStoragePartitionForSite(browser_context_, site_url);
     std::string storage_domain;
     auto* site_instance = rfh->GetSiteInstance();
     if (site_instance) {
@@ -1195,10 +1192,8 @@ void DownloadManagerImpl::BeginResourceDownloadOnChecksComplete(
             params->url(), rfh, /*is_navigation=*/false,
             storage_partition->GetFileSystemContext(), storage_domain);
   } else {
-    StoragePartitionImpl* storage_partition =
-        static_cast<StoragePartitionImpl*>(
-            BrowserContext::GetStoragePartitionForSite(browser_context_,
-                                                       site_url));
+    StoragePartition* storage_partition =
+        BrowserContext::GetStoragePartitionForSite(browser_context_, site_url);
     url_loader_factory_getter =
         CreateDownloadURLLoaderFactoryGetter(storage_partition, rfh, true);
   }
diff --git content/browser/loader/navigation_url_loader_impl.cc content/browser/loader/navigation_url_loader_impl.cc
index d9034953e7f8..0e7c34daa4f8 100644
--- content/browser/loader/navigation_url_loader_impl.cc
+++ content/browser/loader/navigation_url_loader_impl.cc
@@ -1131,7 +1131,7 @@ class NavigationURLLoaderImpl::URLLoaderRequestController
     // path does as well for navigations.
     bool has_plugin = PluginService::GetInstance()->GetPluginInfo(
         -1 /* render_process_id */, -1 /* render_frame_id */, resource_context_,
-        resource_request_->url, url::Origin(), head.mime_type,
+        resource_request_->url, true, url::Origin(), head.mime_type,
         false /* allow_wildcard */, &stale, &plugin, nullptr);
 
     if (stale) {
@@ -1495,7 +1495,7 @@ NavigationURLLoaderImpl::NavigationURLLoaderImpl(
   network::mojom::URLLoaderFactoryPtrInfo proxied_factory_info;
   network::mojom::URLLoaderFactoryRequest proxied_factory_request;
   bool bypass_redirect_checks = false;
-  auto* partition = static_cast<StoragePartitionImpl*>(storage_partition);
+  auto* partition = storage_partition;
   if (frame_tree_node) {
     // |frame_tree_node| may be null in some unit test environments.
     GetContentClient()
diff --git content/browser/payments/payment_app_installer.cc content/browser/payments/payment_app_installer.cc
index 6a6e31bdb070..dce0433e1775 100644
--- content/browser/payments/payment_app_installer.cc
+++ content/browser/payments/payment_app_installer.cc
@@ -125,9 +125,9 @@ class SelfDeleteInstaller
   void SetPaymentAppIntoDatabase() {
     DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-    StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
+    StoragePartition* partition =
         BrowserContext::GetDefaultStoragePartition(
-            web_contents()->GetBrowserContext()));
+            web_contents()->GetBrowserContext());
     scoped_refptr<PaymentAppContextImpl> payment_app_context =
         partition->GetPaymentAppContext();
 
diff --git content/browser/payments/payment_app_provider_impl.cc content/browser/payments/payment_app_provider_impl.cc
index 3cfa0bde2bca..96da49496944 100644
--- content/browser/payments/payment_app_provider_impl.cc
+++ content/browser/payments/payment_app_provider_impl.cc
@@ -369,10 +369,11 @@ void StartServiceWorkerForDispatch(BrowserContext* browser_context,
                                    ServiceWorkerStartCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
-      BrowserContext::GetDefaultStoragePartition(browser_context));
+  StoragePartition* partition =
+      BrowserContext::GetDefaultStoragePartition(browser_context);
   scoped_refptr<ServiceWorkerContextWrapper> service_worker_context =
-      partition->GetServiceWorkerContext();
+      static_cast<ServiceWorkerContextWrapper*>(
+          partition->GetServiceWorkerContext());
 
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
@@ -446,8 +447,8 @@ void PaymentAppProviderImpl::GetAllPaymentApps(
     GetAllPaymentAppsCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
-      BrowserContext::GetDefaultStoragePartition(browser_context));
+  StoragePartition* partition =
+      BrowserContext::GetDefaultStoragePartition(browser_context);
   scoped_refptr<PaymentAppContextImpl> payment_app_context =
       partition->GetPaymentAppContext();
 
diff --git content/browser/renderer_host/render_process_host_impl.cc content/browser/renderer_host/render_process_host_impl.cc
index 989b52793c48..a9c5e6c9755b 100644
--- content/browser/renderer_host/render_process_host_impl.cc
+++ content/browser/renderer_host/render_process_host_impl.cc
@@ -739,11 +739,10 @@ class DefaultSubframeProcessHostHolder : public base::SupportsUserData::Data,
   // Gets the correct render process to use for this SiteInstance.
   RenderProcessHost* GetProcessHost(SiteInstance* site_instance,
                                     bool is_for_guests_only) {
-    StoragePartitionImpl* default_partition =
-        static_cast<StoragePartitionImpl*>(
-            BrowserContext::GetDefaultStoragePartition(browser_context_));
-    StoragePartitionImpl* partition = static_cast<StoragePartitionImpl*>(
-        BrowserContext::GetStoragePartition(browser_context_, site_instance));
+    StoragePartition* default_partition =
+        BrowserContext::GetDefaultStoragePartition(browser_context_);
+    StoragePartition* partition =
+        BrowserContext::GetStoragePartition(browser_context_, site_instance);
 
     // Is this the default storage partition? If it isn't, then just give it its
     // own non-shared process.
@@ -1474,7 +1473,7 @@ int RenderProcessHost::GetCurrentRenderProcessCountForTesting() {
 // static
 RenderProcessHost* RenderProcessHostImpl::CreateRenderProcessHost(
     BrowserContext* browser_context,
-    StoragePartitionImpl* storage_partition_impl,
+    StoragePartition* storage_partition_impl,
     SiteInstance* site_instance,
     bool is_for_guests_only) {
   if (g_render_process_host_factory_) {
@@ -1483,8 +1482,8 @@ RenderProcessHost* RenderProcessHostImpl::CreateRenderProcessHost(
   }
 
   if (!storage_partition_impl) {
-    storage_partition_impl = static_cast<StoragePartitionImpl*>(
-        BrowserContext::GetStoragePartition(browser_context, site_instance));
+    storage_partition_impl =
+        BrowserContext::GetStoragePartition(browser_context, site_instance);
   }
   // If we've made a StoragePartition for guests (e.g., for the <webview> tag),
   // stash the Site URL on it. This way, when we start a service worker inside
@@ -1509,7 +1508,7 @@ const unsigned int RenderProcessHostImpl::kMaxFrameDepthForPriority =
 
 RenderProcessHostImpl::RenderProcessHostImpl(
     BrowserContext* browser_context,
-    StoragePartitionImpl* storage_partition_impl,
+    StoragePartition* storage_partition_impl,
     bool is_for_guests_only)
     : fast_shutdown_started_(false),
       deleting_soon_(false),
@@ -1562,10 +1561,12 @@ RenderProcessHostImpl::RenderProcessHostImpl(
       indexed_db_factory_(new IndexedDBDispatcherHost(
           id_,
           storage_partition_impl_->GetURLRequestContext(),
-          storage_partition_impl_->GetIndexedDBContext(),
+          static_cast<IndexedDBContextImpl*>(
+              storage_partition_impl_->GetIndexedDBContext()),
           ChromeBlobStorageContext::GetFor(browser_context_))),
       service_worker_dispatcher_host_(new ServiceWorkerDispatcherHost(
-          storage_partition_impl_->GetServiceWorkerContext(),
+          static_cast<ServiceWorkerContextWrapper*>(
+              storage_partition_impl_->GetServiceWorkerContext()),
           id_)),
       channel_connected_(false),
       sent_render_process_ready_(false),
@@ -1600,7 +1601,8 @@ RenderProcessHostImpl::RenderProcessHostImpl(
   }
 
   push_messaging_manager_.reset(new PushMessagingManager(
-      GetID(), storage_partition_impl_->GetServiceWorkerContext()));
+      GetID(), static_cast<ServiceWorkerContextWrapper*>(
+          storage_partition_impl_->GetServiceWorkerContext())));
 
   AddObserver(indexed_db_factory_.get());
   AddObserver(service_worker_dispatcher_host_.get());
@@ -1936,6 +1938,17 @@ void RenderProcessHostImpl::ResetChannelProxy() {
 
 void RenderProcessHostImpl::CreateMessageFilters() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  // Cast to the derived type from StoragePartitionImpl.
+  auto app_cache_service = static_cast<ChromeAppCacheService*>(
+      storage_partition_impl_->GetAppCacheService());
+  auto cache_storage_context = static_cast<CacheStorageContextImpl*>(
+      storage_partition_impl_->GetCacheStorageContext());
+  auto dom_storage_context = static_cast<DOMStorageContextWrapper*>(
+      storage_partition_impl_->GetDOMStorageContext());
+  auto service_worker_context = static_cast<ServiceWorkerContextWrapper*>(
+      storage_partition_impl_->GetServiceWorkerContext());
+
   MediaInternals* media_internals = MediaInternals::GetInstance();
   // Add BrowserPluginMessageFilter to ensure it gets the first stab at messages
   // from guests.
@@ -1950,7 +1963,7 @@ void RenderProcessHostImpl::CreateMessageFilters() {
       base::MakeRefCounted<RenderMessageFilter>(
           GetID(), GetBrowserContext(), request_context.get(),
           widget_helper_.get(), media_internals,
-          storage_partition_impl_->GetCacheStorageContext(),
+          cache_storage_context,
           storage_partition_impl_->GetGeneratedCodeCacheContext());
   AddFilter(render_message_filter.get());
 
@@ -1978,10 +1991,10 @@ void RenderProcessHostImpl::CreateMessageFilters() {
       ChromeBlobStorageContext::GetFor(browser_context);
 
   resource_message_filter_ = new ResourceMessageFilter(
-      GetID(), storage_partition_impl_->GetAppCacheService(),
+      GetID(), app_cache_service,
       blob_storage_context.get(),
       storage_partition_impl_->GetFileSystemContext(),
-      storage_partition_impl_->GetServiceWorkerContext(),
+      service_worker_context,
       storage_partition_impl_->GetPrefetchURLLoaderService(),
       std::move(get_contexts_callback),
       BrowserThread::GetTaskRunnerForThread(BrowserThread::IO));
@@ -1990,8 +2003,7 @@ void RenderProcessHostImpl::CreateMessageFilters() {
 
   AddFilter(
       new MidiHost(GetID(), BrowserMainLoop::GetInstance()->midi_service()));
-  AddFilter(new DOMStorageMessageFilter(
-      storage_partition_impl_->GetDOMStorageContext()));
+  AddFilter(new DOMStorageMessageFilter(dom_storage_context));
 
   peer_connection_tracker_host_ = new PeerConnectionTrackerHost(GetID());
   AddFilter(peer_connection_tracker_host_.get());
@@ -2008,10 +2020,6 @@ void RenderProcessHostImpl::CreateMessageFilters() {
 
   AddFilter(new TraceMessageFilter(GetID()));
   AddFilter(new ResolveProxyMsgHelper(GetID()));
-
-  scoped_refptr<ServiceWorkerContextWrapper> service_worker_context(
-      static_cast<ServiceWorkerContextWrapper*>(
-          storage_partition_impl_->GetServiceWorkerContext()));
 }
 
 void RenderProcessHostImpl::BindCacheStorage(
@@ -2023,7 +2031,8 @@ void RenderProcessHostImpl::BindCacheStorage(
     cache_storage_dispatcher_host_ =
         base::MakeRefCounted<CacheStorageDispatcherHost>();
     cache_storage_dispatcher_host_->Init(
-        storage_partition_impl_->GetCacheStorageContext());
+        static_cast<CacheStorageContextImpl*>(
+            storage_partition_impl_->GetCacheStorageContext()));
   }
   // Send the binding to IO thread, because Cache Storage handles Mojo IPC on IO
   // thread entirely.
@@ -2198,7 +2207,8 @@ void RenderProcessHostImpl::RegisterMojoInterfaces() {
 
   registry->AddInterface(base::BindRepeating(
       &AppCacheDispatcherHost::Create,
-      base::Unretained(storage_partition_impl_->GetAppCacheService()),
+      base::Unretained(static_cast<ChromeAppCacheService*>(
+          storage_partition_impl_->GetAppCacheService())),
       GetID()));
 
   AddUIThreadInterface(
@@ -2235,6 +2245,9 @@ void RenderProcessHostImpl::RegisterMojoInterfaces() {
     plugin_registry_.reset(
         new PluginRegistryImpl(GetBrowserContext()->GetResourceContext()));
   }
+  // Needed for proper routing of IsPluginAvailable callbacks.
+  DCHECK_GE(GetID(), 0);
+  plugin_registry_->set_render_process_id(GetID());
   registry->AddInterface(base::BindRepeating(
       &PluginRegistryImpl::Bind, base::Unretained(plugin_registry_.get())));
 #endif
diff --git content/browser/renderer_host/render_process_host_impl.h content/browser/renderer_host/render_process_host_impl.h
index 37bc9b79afd7..ed496b1c7439 100644
--- content/browser/renderer_host/render_process_host_impl.h
+++ content/browser/renderer_host/render_process_host_impl.h
@@ -97,7 +97,6 @@ class ServiceWorkerDispatcherHost;
 class SiteInstance;
 class SiteInstanceImpl;
 class StoragePartition;
-class StoragePartitionImpl;
 struct ChildProcessTerminationInfo;
 
 typedef base::Thread* (*RendererMainThreadFactoryFunction)(
@@ -140,7 +139,7 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // null.
   static RenderProcessHost* CreateRenderProcessHost(
       BrowserContext* browser_context,
-      StoragePartitionImpl* storage_partition_impl,
+      StoragePartition* storage_partition_impl,
       SiteInstance* site_instance,
       bool is_for_guests_only);
 
@@ -484,7 +483,7 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // Use CreateRenderProcessHost() instead of calling this constructor
   // directly.
   RenderProcessHostImpl(BrowserContext* browser_context,
-                        StoragePartitionImpl* storage_partition_impl,
+                        StoragePartition* storage_partition_impl,
                         bool is_for_guests_only);
 
   // Initializes a new IPC::ChannelProxy in |channel_|, which will be connected
@@ -753,10 +752,10 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // called.
   int instance_id_ = 1;
 
-  BrowserContext* const browser_context_;
+  BrowserContext* browser_context_;
 
   // Owned by |browser_context_|.
-  StoragePartitionImpl* storage_partition_impl_;
+  StoragePartition* storage_partition_impl_;
 
   // The observers watching our lifetime.
   base::ObserverList<RenderProcessHostObserver>::Unchecked observers_;
diff --git content/browser/renderer_interface_binders.cc content/browser/renderer_interface_binders.cc
index c3a8bdc572de..73f66acbe200 100644
--- content/browser/renderer_interface_binders.cc
+++ content/browser/renderer_interface_binders.cc
@@ -139,7 +139,7 @@ void RendererInterfaceBinders::InitializeParameterizedBinderRegistry() {
   parameterized_binder_registry_.AddInterface(
       base::Bind([](payments::mojom::PaymentManagerRequest request,
                     RenderProcessHost* host, const url::Origin& origin) {
-        static_cast<StoragePartitionImpl*>(host->GetStoragePartition())
+        host->GetStoragePartition()
             ->GetPaymentAppContext()
             ->CreatePaymentManager(std::move(request));
       }));
@@ -159,15 +159,16 @@ void RendererInterfaceBinders::InitializeParameterizedBinderRegistry() {
   parameterized_binder_registry_.AddInterface(base::BindRepeating(
       [](blink::mojom::LockManagerRequest request, RenderProcessHost* host,
          const url::Origin& origin) {
-        static_cast<StoragePartitionImpl*>(host->GetStoragePartition())
+        host->GetStoragePartition()
             ->GetLockManager()
             ->CreateService(std::move(request), origin);
       }));
   parameterized_binder_registry_.AddInterface(
       base::Bind([](blink::mojom::NotificationServiceRequest request,
                     RenderProcessHost* host, const url::Origin& origin) {
-        static_cast<StoragePartitionImpl*>(host->GetStoragePartition())
-            ->GetPlatformNotificationContext()
+        static_cast<PlatformNotificationContextImpl*>(
+        host->GetStoragePartition()
+            ->GetPlatformNotificationContext())
             ->CreateService(origin, std::move(request));
       }));
   parameterized_binder_registry_.AddInterface(
@@ -179,7 +180,7 @@ void RendererInterfaceBinders::InitializeParameterizedBinderRegistry() {
   parameterized_binder_registry_.AddInterface(base::BindRepeating(
       [](blink::mojom::CookieStoreRequest request, RenderProcessHost* host,
          const url::Origin& origin) {
-        static_cast<StoragePartitionImpl*>(host->GetStoragePartition())
+        host->GetStoragePartition()
             ->GetCookieStoreContext()
             ->CreateService(std::move(request), origin);
       }));
diff --git content/browser/shared_worker/shared_worker_connector_impl.cc content/browser/shared_worker/shared_worker_connector_impl.cc
index 2fe70f50171f..98244cd5ddf8 100644
--- content/browser/shared_worker/shared_worker_connector_impl.cc
+++ content/browser/shared_worker/shared_worker_connector_impl.cc
@@ -52,8 +52,8 @@ void SharedWorkerConnectorImpl::Connect(
             host->GetBrowserContext(), std::move(blob_url_token));
   }
   SharedWorkerServiceImpl* service =
-      static_cast<StoragePartitionImpl*>(host->GetStoragePartition())
-          ->GetSharedWorkerService();
+      static_cast<SharedWorkerServiceImpl*>(host->GetStoragePartition()
+          ->GetSharedWorkerService());
   service->ConnectToWorker(process_id_, frame_id_, std::move(info),
                            std::move(client), creation_context_type,
                            blink::MessagePortChannel(std::move(message_port)),
diff --git content/browser/shared_worker/shared_worker_service_impl.cc content/browser/shared_worker/shared_worker_service_impl.cc
index 51f91bdd7e2f..a67745058ed3 100644
--- content/browser/shared_worker/shared_worker_service_impl.cc
+++ content/browser/shared_worker/shared_worker_service_impl.cc
@@ -344,8 +344,8 @@ void SharedWorkerServiceImpl::CreateWorker(
         BrowserThread::IO, FROM_HERE,
         base::BindOnce(
             &CreateScriptLoaderOnIO,
-            service_worker_context_->storage_partition()
-                ->url_loader_factory_getter(),
+            base::WrapRefCounted(service_worker_context_->storage_partition()
+                ->url_loader_factory_getter()),
             std::move(factory_bundle_for_browser),
             std::move(subresource_loader_factories), service_worker_context_,
             appcache_handle_core,
diff --git content/browser/storage_partition_impl.h content/browser/storage_partition_impl.h
index 6f6c5c1e504a..097095a613dd 100644
--- content/browser/storage_partition_impl.h
+++ content/browser/storage_partition_impl.h
@@ -95,7 +95,7 @@ class CONTENT_EXPORT StoragePartitionImpl
   storage::FileSystemContext* GetFileSystemContext() override;
   storage::DatabaseTracker* GetDatabaseTracker() override;
   DOMStorageContextWrapper* GetDOMStorageContext() override;
-  LockManager* GetLockManager();  // override; TODO: Add to interface
+  LockManager* GetLockManager() override;
   IndexedDBContextImpl* GetIndexedDBContext() override;
   CacheStorageContextImpl* GetCacheStorageContext() override;
   ServiceWorkerContextWrapper* GetServiceWorkerContext() override;
@@ -136,14 +136,14 @@ class CONTENT_EXPORT StoragePartitionImpl
   void FlushNetworkInterfaceForTesting() override;
   void WaitForDeletionTasksForTesting() override;
 
-  BackgroundFetchContext* GetBackgroundFetchContext();
-  BackgroundSyncContext* GetBackgroundSyncContext();
-  PaymentAppContextImpl* GetPaymentAppContext();
-  BroadcastChannelProvider* GetBroadcastChannelProvider();
-  BluetoothAllowedDevicesMap* GetBluetoothAllowedDevicesMap();
-  BlobRegistryWrapper* GetBlobRegistry();
-  PrefetchURLLoaderService* GetPrefetchURLLoaderService();
-  CookieStoreContext* GetCookieStoreContext();
+  BackgroundFetchContext* GetBackgroundFetchContext() override;
+  BackgroundSyncContext* GetBackgroundSyncContext() override;
+  PaymentAppContextImpl* GetPaymentAppContext() override;
+  BroadcastChannelProvider* GetBroadcastChannelProvider() override;
+  BluetoothAllowedDevicesMap* GetBluetoothAllowedDevicesMap() override;
+  BlobRegistryWrapper* GetBlobRegistry() override;
+  PrefetchURLLoaderService* GetPrefetchURLLoaderService() override;
+  CookieStoreContext* GetCookieStoreContext() override;
 
   // blink::mojom::StoragePartitionService interface.
   void OpenLocalStorage(const url::Origin& origin,
@@ -152,18 +152,19 @@ class CONTENT_EXPORT StoragePartitionImpl
       const std::string& namespace_id,
       blink::mojom::SessionStorageNamespaceRequest request) override;
 
-  scoped_refptr<URLLoaderFactoryGetter> url_loader_factory_getter() {
-    return url_loader_factory_getter_;
+  URLLoaderFactoryGetter* url_loader_factory_getter() override {
+    return url_loader_factory_getter_.get();
   }
 
   // Can return nullptr while |this| is being destroyed.
-  BrowserContext* browser_context() const;
+  BrowserContext* browser_context() const override;
 
   // Called by each renderer process once. Returns the id of the created
   // binding.
   mojo::BindingId Bind(
       int process_id,
-      mojo::InterfaceRequest<blink::mojom::StoragePartitionService> request);
+      mojo::InterfaceRequest<blink::mojom::StoragePartitionService> request)
+      override;
 
   auto& bindings_for_testing() { return bindings_; }
 
@@ -174,10 +175,11 @@ class CONTENT_EXPORT StoragePartitionImpl
   // one must use the "chrome-guest://blahblah" site URL to ensure that the
   // service worker stays in this StoragePartition. This is an empty GURL if
   // this StoragePartition is not for guests.
-  void set_site_for_service_worker(const GURL& site_for_service_worker) {
+  void set_site_for_service_worker(
+      const GURL& site_for_service_worker) override {
     site_for_service_worker_ = site_for_service_worker;
   }
-  const GURL& site_for_service_worker() const {
+  const GURL& site_for_service_worker() const override {
     return site_for_service_worker_;
   }
 
diff --git content/browser/streams/stream_context.cc content/browser/streams/stream_context.cc
index 0ab6a2d6f963..f24e547f2396 100644
--- content/browser/streams/stream_context.cc
+++ content/browser/streams/stream_context.cc
@@ -21,6 +21,11 @@ namespace content {
 
 StreamContext::StreamContext() {}
 
+// static
+const void* StreamContext::GetUserDataKey() {
+  return kStreamContextKeyName;
+}
+
 StreamContext* StreamContext::GetFor(BrowserContext* context) {
   if (!context->GetUserData(kStreamContextKeyName)) {
     scoped_refptr<StreamContext> stream = new StreamContext();
diff --git content/browser/streams/stream_context.h content/browser/streams/stream_context.h
index 075ae3e7431e..57fb5fd2c4a8 100644
--- content/browser/streams/stream_context.h
+++ content/browser/streams/stream_context.h
@@ -29,6 +29,7 @@ class StreamContext
  public:
   StreamContext();
 
+  CONTENT_EXPORT static const void* GetUserDataKey();
   CONTENT_EXPORT static StreamContext* GetFor(BrowserContext* browser_context);
 
   void InitializeOnIOThread();
diff --git content/browser/webui/web_ui_url_loader_factory.cc content/browser/webui/web_ui_url_loader_factory.cc
index a0e398098383..5ea5de0df6c2 100644
--- content/browser/webui/web_ui_url_loader_factory.cc
+++ content/browser/webui/web_ui_url_loader_factory.cc
@@ -19,13 +19,13 @@
 #include "content/browser/blob_storage/chrome_blob_storage_context.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
 #include "content/browser/resource_context_impl.h"
-#include "content/browser/storage_partition_impl.h"
 #include "content/browser/webui/network_error_url_loader.h"
 #include "content/browser/webui/url_data_manager_backend.h"
 #include "content/browser/webui/url_data_source_impl.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/render_process_host.h"
+#include "content/public/browser/storage_partition.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/common/url_constants.h"
@@ -313,9 +313,8 @@ class WebUIURLLoaderFactory : public network::mojom::URLLoaderFactory,
   const std::string& scheme() const { return scheme_; }
 
  private:
-  StoragePartitionImpl* GetStoragePartition() {
-    return static_cast<StoragePartitionImpl*>(
-        render_frame_host_->GetProcess()->GetStoragePartition());
+  StoragePartition* GetStoragePartition() {
+    return render_frame_host_->GetProcess()->GetStoragePartition();
   }
 
   RenderFrameHost* render_frame_host_;
diff --git content/public/browser/browser_context.h content/public/browser/browser_context.h
index e49eaaa04abb..0c13d6a95a4d 100644
--- content/public/browser/browser_context.h
+++ content/public/browser/browser_context.h
@@ -217,6 +217,8 @@ class CONTENT_EXPORT BrowserContext : public base::SupportsUserData {
 
   BrowserContext();
 
+  static const void* GetStoragePartitionMapUserDataKey();
+
   ~BrowserContext() override;
 
   // Shuts down the storage partitions associated to this browser context.
@@ -311,6 +313,14 @@ class CONTENT_EXPORT BrowserContext : public base::SupportsUserData {
           const base::FilePath& partition_path,
           bool in_memory) = 0;
 
+  // CEF returns a proxy object that forwards method calls to |partition_impl|.
+  virtual content::StoragePartition* GetStoragePartitionProxy(
+      BrowserContext* browser_context,
+      content::StoragePartition* partition_impl) {
+    NOTREACHED();
+    return nullptr;
+  }
+
   using StaticServiceMap =
       std::map<std::string, service_manager::EmbeddedServiceInfo>;
 
diff --git content/public/browser/storage_partition.h content/public/browser/storage_partition.h
index f55e28d79cda..297541d0a99a 100644
--- content/public/browser/storage_partition.h
+++ content/public/browser/storage_partition.h
@@ -14,8 +14,10 @@
 #include "base/files/file_path.h"
 #include "base/time/time.h"
 #include "content/common/content_export.h"
+#include "mojo/public/cpp/bindings/binding_set.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "services/network/public/mojom/cookie_manager.mojom.h"
+#include "third_party/blink/public/mojom/dom_storage/storage_partition_service.mojom.h"
 
 class GURL;
 
@@ -60,12 +62,28 @@ class ServiceWorkerContext;
 class SharedWorkerService;
 class WebPackageContext;
 
+class BackgroundFetchContext;
+class BackgroundSyncContext;
+class BlobRegistryWrapper;
+class BlobURLLoaderFactory;
+class BluetoothAllowedDevicesMap;
+class BroadcastChannelProvider;
+class CookieStoreContext;
+class LockManager;
+class PaymentAppContextImpl;
+class PrefetchURLLoaderService;
+class URLLoaderFactoryGetter;
+
 #if !defined(OS_ANDROID)
 class HostZoomLevelContext;
 class HostZoomMap;
 class ZoomLevelDelegate;
 #endif  // !defined(OS_ANDROID)
 
+namespace mojom {
+class StoragePartitionService;
+}
+
 // Defines what persistent state a child process can access.
 //
 // The StoragePartition defines the view each child process has of the
@@ -103,6 +121,7 @@ class CONTENT_EXPORT StoragePartition {
   virtual storage::FileSystemContext* GetFileSystemContext() = 0;
   virtual storage::DatabaseTracker* GetDatabaseTracker() = 0;
   virtual DOMStorageContext* GetDOMStorageContext() = 0;
+  virtual LockManager* GetLockManager() = 0;
   virtual IndexedDBContext* GetIndexedDBContext() = 0;
   virtual ServiceWorkerContext* GetServiceWorkerContext() = 0;
   virtual SharedWorkerService* GetSharedWorkerService() = 0;
@@ -229,6 +248,26 @@ class CONTENT_EXPORT StoragePartition {
   // Wait until all deletions tasks are finished. For test use only.
   virtual void WaitForDeletionTasksForTesting() = 0;
 
+  virtual BackgroundFetchContext* GetBackgroundFetchContext() = 0;
+  virtual BackgroundSyncContext* GetBackgroundSyncContext() = 0;
+  virtual PaymentAppContextImpl* GetPaymentAppContext() = 0;
+  virtual BroadcastChannelProvider* GetBroadcastChannelProvider() = 0;
+  virtual BluetoothAllowedDevicesMap* GetBluetoothAllowedDevicesMap() = 0;
+  virtual BlobRegistryWrapper* GetBlobRegistry() = 0;
+  virtual PrefetchURLLoaderService* GetPrefetchURLLoaderService() = 0;
+  virtual CookieStoreContext* GetCookieStoreContext() = 0;
+
+  virtual URLLoaderFactoryGetter* url_loader_factory_getter() = 0;
+  virtual BrowserContext* browser_context() const = 0;
+
+  virtual mojo::BindingId Bind(
+      int process_id,
+      mojo::InterfaceRequest<blink::mojom::StoragePartitionService> request) = 0;
+      
+  virtual void set_site_for_service_worker(
+      const GURL& site_for_service_worker) = 0;
+  virtual const GURL& site_for_service_worker() const = 0;
+
  protected:
   virtual ~StoragePartition() {}
 };
diff --git storage/browser/database/database_tracker.cc storage/browser/database/database_tracker.cc
index e18b8180bb5e..f775176238ac 100644
--- storage/browser/database/database_tracker.cc
+++ storage/browser/database/database_tracker.cc
@@ -481,7 +481,7 @@ bool DatabaseTracker::LazyInit() {
     meta_table_.reset(new sql::MetaTable());
 
     is_initialized_ =
-        base::CreateDirectory(db_dir_) &&
+        (is_incognito_ ? true : base::CreateDirectory(db_dir_)) &&
         (db_->is_open() ||
          (is_incognito_ ? db_->OpenInMemory() :
           db_->Open(kTrackerDatabaseFullPath))) &&