diff --git content/browser/web_contents/web_contents_view.h content/browser/web_contents/web_contents_view.h
index dc763b0fac47b..d8b63a0f62267 100644
--- content/browser/web_contents/web_contents_view.h
+++ content/browser/web_contents/web_contents_view.h
@@ -25,7 +25,7 @@ struct DropData;
 // The `WebContentsView` is an interface that is implemented by the platform-
 // dependent web contents views. The `WebContents` uses this interface to talk
 // to them.
-class WebContentsView {
+class CONTENT_EXPORT WebContentsView {
  public:
   virtual ~WebContentsView() = default;
 
diff --git extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
index 0fc4a40faf070..66b40489529e2 100644
--- extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
+++ extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
@@ -202,6 +202,8 @@ void MimeHandlerViewGuest::CreateWebContents(
   WebContents::CreateParams params(browser_context(),
                                    guest_site_instance.get());
   params.guest_delegate = this;
+  if (delegate_)
+    delegate_->OverrideWebContentsCreateParams(&params);
   std::move(callback).Run(std::move(owned_this),
                           WebContents::CreateWithSessionStorage(
                               params, owner_web_contents()
@@ -210,6 +212,10 @@ void MimeHandlerViewGuest::CreateWebContents(
 }
 
 void MimeHandlerViewGuest::DidAttachToEmbedder() {
+  is_guest_attached_ = true;
+  if (delegate_)
+    delegate_->OnGuestAttached();
+
   DCHECK(stream_->handler_url().SchemeIs(extensions::kExtensionScheme));
   GetController().LoadURL(stream_->handler_url(), content::Referrer(),
                           ui::PAGE_TRANSITION_AUTO_TOPLEVEL, std::string());
@@ -474,6 +480,14 @@ void MimeHandlerViewGuest::DidFinishNavigation(
   }
 }
 
+void MimeHandlerViewGuest::WebContentsDestroyed() {
+  if (is_guest_attached_ && delegate_)
+    delegate_->OnGuestDetached();
+
+  // May delete |this|.
+  GuestView<MimeHandlerViewGuest>::WebContentsDestroyed();
+}
+
 void MimeHandlerViewGuest::FuseBeforeUnloadControl(
     mojo::PendingReceiver<mime_handler::BeforeUnloadControl> receiver) {
   if (!pending_before_unload_control_)
diff --git extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
index 2a2f0b6b44293..b5a5e9949138f 100644
--- extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
+++ extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
@@ -194,10 +194,12 @@ class MimeHandlerViewGuest
   void ReadyToCommitNavigation(
       content::NavigationHandle* navigation_handle) final;
   void DidFinishNavigation(content::NavigationHandle* navigation_handle) final;
+  void WebContentsDestroyed() override;
 
   std::unique_ptr<MimeHandlerViewGuestDelegate> delegate_;
   std::unique_ptr<StreamContainer> stream_;
 
+  bool is_guest_attached_ = false;
   bool is_guest_fullscreen_ = false;
   bool is_embedder_fullscreen_ = false;
   bool plugin_can_save_ = false;
diff --git extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest_delegate.h extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest_delegate.h
index 7f59e7925084e..777b8a3cf103a 100644
--- extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest_delegate.h
+++ extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest_delegate.h
@@ -7,6 +7,8 @@
 
 #include <string>
 
+#include "content/public/browser/web_contents.h"
+
 namespace content {
 class RenderFrameHost;
 struct ContextMenuParams;
@@ -25,6 +27,14 @@ class MimeHandlerViewGuestDelegate {
 
   virtual ~MimeHandlerViewGuestDelegate() {}
 
+  // Provides an opportunity to supply a custom view implementation.
+  virtual void OverrideWebContentsCreateParams(
+      content::WebContents::CreateParams* params) {}
+
+  // Called when a guest is attached or detached.
+  virtual void OnGuestAttached() {}
+  virtual void OnGuestDetached() {}
+
   // Handles context menu, or returns false if unhandled.
   //
   // The `render_frame_host` represents the frame that requests the context menu