Use observer pattern instead of sniffing SwapCompositorFrame IPC

content/public/test/browser_test_utils.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_TEST_BROWSER_TEST_UTILS_H_
 #define CONTENT_PUBLIC_TEST_BROWSER_TEST_UTILS_H_
 
 #include <queue>
 #include <string>
 #include <vector>
@@ skipping 513 matching lines @@
   std::unique_ptr<RenderViewCreatedObserver> child_observer_;
   scoped_refptr<MessageLoopRunner> runner_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsAddedObserver);
 };
 
 // Request a new frame be drawn, returns false if request fails.
 bool RequestFrame(WebContents* web_contents);
 
 // Watches compositor frame changes, blocking until a frame has been
-// composited. This class is intended to be run on the main thread; to
-// synchronize the main thread against the impl thread.
-class FrameWatcher : public IPC::MessageFilter {
+// composited. This class must run on the UI thread.
+class FrameWatcher : public WebContentsObserver {
  public:
+  // Don't observe any WebContents at construction. Observe() must be called
+  // later on.
   FrameWatcher();
 
-  // Listen for new frames from the |web_contents| renderer process.
-  void AttachTo(WebContents* web_contents);
+  // Listen for new frames from the |web_contents| renderer process. The
+  // WebContents that we observe can be changed by calling Observe().
+  FrameWatcher(WebContents* web_contents);

[piman, 2017/04/04 17:34:46]

nit: explicit

[Saman Sami, 2017/04/04 17:49:54]

Done.

+
+  ~FrameWatcher() override;
 
   // Wait for |frames_to_wait| swap mesages from the compositor.
   void WaitFrames(int frames_to_wait);
 
-  // Return the meta data received in the last compositor
-  // swap frame.
+  // Return the last received CompositorFrame's metadata.
   const cc::CompositorFrameMetadata& LastMetadata();
 
+  // Call this method to start observing a WebContents for CompositorFrames.
+  using WebContentsObserver::Observe;
+
  private:
-  ~FrameWatcher() override;
+  // WebContentsObserver implementation.
+  void DidReceiveCompositorFrame() override;
 
-  // Overridden BrowserMessageFilter methods.
-  bool OnMessageReceived(const IPC::Message& message) override;
-
-  void ReceivedFrameSwap(cc::CompositorFrameMetadata meta_data);
-
-  int frames_to_wait_;
+  int frames_to_wait_ = 0;
   base::Closure quit_;
-  cc::CompositorFrameMetadata last_metadata_;
 
   DISALLOW_COPY_AND_ASSIGN(FrameWatcher);
 };
 
 // This class is intended to synchronize the renderer main thread, renderer impl
 // thread and the browser main thread.
 class MainThreadFrameObserver : public IPC::Listener {
  public:
   explicit MainThreadFrameObserver(RenderWidgetHost* render_widget_host);
   ~MainThreadFrameObserver() override;
@@ skipping 229 matching lines @@
 
  private:
   PwnMessageHelper();  // Not instantiable.
 
   DISALLOW_COPY_AND_ASSIGN(PwnMessageHelper);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_TEST_BROWSER_TEST_UTILS_H_