Add CefFrameHandler callbacks for tracking CefFrame lifespan (see issue #2421)

See the new cef_frame_handler.h for complete usage documentation.

This change includes the following related enhancements:
- The newly added CefBrowser::IsValid method will return false (in the browser
  process) after CefLifeSpanHandler::OnBeforeClose is called.
- CefBrowser::GetMainFrame will return a valid object (in the browser process)
  until after CefLifeSpanHandler::OnBeforeClose is called.
- The main frame object will change during cross-origin navigation or
  re-navigation after renderer process termination. During that time,
  GetMainFrame will return the new/pending frame (in the browser process) and
  any messages that arrive for the new/pending frame will be correctly
  attributed in OnProcessMessageReceived.
- Commands to be executed in the renderer process that may fail during early
  frame initialization (ExecuteJavaScript, LoadRequest, etc.) will now be
  queued until after the JavaScript context for the frame has been created.
- Logging has been added for any commands that are dropped because they arrived
  after frame detachment.

libcef/browser/browser_info.h

@@ -6,6 +6,7 @@
 #define CEF_LIBCEF_BROWSER_BROWSER_INFO_H_
 #pragma once
 
+#include <queue>
 #include <set>
 #include <unordered_map>
 
@@ -24,6 +25,7 @@ class RenderFrameHost;
 }
 
 class CefBrowserHostBase;
+class CefFrameHandler;
 class CefFrameHostImpl;
 
 // CefBrowserInfo is used to associate a browser ID and render view/process
@@ -149,6 +151,16 @@ class CefBrowserInfo : public base::RefCountedThreadSafe<CefBrowserInfo> {
   // thread.
   bool IsNavigationLocked(base::OnceClosure pending_action);
 
+  using FrameNotifyOnceAction =
+      base::OnceCallback<void(CefRefPtr<CefFrameHandler>)>;
+
+  // Specifies a CefFrameHandler notification action whose execution may need
+  // to be blocked on release of a potentially held NotificationStateLock. If no
+  // CefFrameHandler exists then the action will be discarded without executing.
+  // If the NotificationStateLock is not currently held then the action will be
+  // executed immediately.
+  void MaybeExecuteFrameNotification(FrameNotifyOnceAction pending_action);
+
  private:
   friend class base::RefCountedThreadSafe<CefBrowserInfo>;
 
@@ -157,6 +169,10 @@ class CefBrowserInfo : public base::RefCountedThreadSafe<CefBrowserInfo> {
   struct FrameInfo {
     ~FrameInfo();
 
+    inline bool IsCurrentMainFrame() const {
+      return frame_ && is_main_frame_ && !is_speculative_;
+    }
+
     content::RenderFrameHost* host_;
     int64_t frame_id_;  // Combination of render_process_id + render_routing_id.
     int frame_tree_node_id_;
@@ -172,7 +188,17 @@ class CefBrowserInfo : public base::RefCountedThreadSafe<CefBrowserInfo> {
       int frame_tree_node_id,
       bool* is_guest_view = nullptr) const;
 
-  void RemoveAllFrames();
+  void SetMainFrame(CefRefPtr<CefBrowserHostBase> browser,
+                    CefRefPtr<CefFrameHostImpl> frame);
+
+  void MaybeNotifyFrameCreated(CefRefPtr<CefFrameHostImpl> frame);
+  void MaybeNotifyFrameDetached(CefRefPtr<CefBrowserHostBase> browser,
+                                CefRefPtr<CefFrameHostImpl> frame);
+  void MaybeNotifyMainFrameChanged(CefRefPtr<CefBrowserHostBase> browser,
+                                   CefRefPtr<CefFrameHostImpl> old_frame,
+                                   CefRefPtr<CefFrameHostImpl> new_frame);
+
+  void RemoveAllFrames(CefRefPtr<CefBrowserHostBase> old_browser);
 
   int browser_id_;
   bool is_popup_;
@@ -183,6 +209,29 @@ class CefBrowserInfo : public base::RefCountedThreadSafe<CefBrowserInfo> {
   // Only accessed on the UI thread.
   base::WeakPtr<NavigationLock> navigation_lock_;
 
+  // Used instead of |base::AutoLock(lock_)| in situations that might generate
+  // CefFrameHandler notifications. Any notifications passed to
+  // MaybeExecuteFrameNotification() will be queued until the lock is released,
+  // and then executed in order.
+  class NotificationStateLock final {
+   public:
+    explicit NotificationStateLock(CefBrowserInfo* browser_info);
+    ~NotificationStateLock();
+
+   protected:
+    friend class CefBrowserInfo;
+    CefBrowserInfo* const browser_info_;
+    CefRefPtr<CefFrameHandler> frame_handler_;
+    std::unique_ptr<base::AutoLock> browser_info_lock_scope_;
+    std::queue<FrameNotifyOnceAction> queue_;
+  };
+
+  mutable base::Lock notification_lock_;
+
+  // These members must be protected by |notification_lock_|.
+  NotificationStateLock* notification_state_lock_ = nullptr;
+  CefRefPtr<CefFrameHandler> frame_handler_;
+
   mutable base::Lock lock_;
 
   // The below members must be protected by |lock_|.