cc: Handle retroactive BeginFrames in the Scheduler.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 2d64a3b8b5c61dc33890e7649eb6688a83b203f5..896670e130bbbe0a8d10f7ff88feb12e4b83cf1e 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -63,7 +63,7 @@ class LayerTreeHostImplClient {
   virtual void DidLoseOutputSurfaceOnImplThread() = 0;
   virtual void DidSwapBuffersOnImplThread() = 0;
   virtual void OnSwapBuffersCompleteOnImplThread() = 0;
-  virtual void BeginImplFrame(const BeginFrameArgs& args) = 0;
+  virtual void BeginFrame(const BeginFrameArgs& args) = 0;
   virtual void OnCanDrawStateChanged(bool can_draw) = 0;
   virtual void NotifyReadyToActivate() = 0;
   // Please call these 2 functions through
@@ -225,7 +225,7 @@ class CC_EXPORT LayerTreeHostImpl
       scoped_refptr<ContextProvider> offscreen_context_provider) OVERRIDE;
   virtual void ReleaseGL() OVERRIDE;
   virtual void SetNeedsRedrawRect(const gfx::Rect& rect) OVERRIDE;
-  virtual void BeginImplFrame(const BeginFrameArgs& args) OVERRIDE;
+  virtual void BeginFrame(const BeginFrameArgs& args) OVERRIDE;
   virtual void SetExternalDrawConstraints(
       const gfx::Transform& transform,
       const gfx::Rect& viewport,
@@ -264,7 +264,8 @@ class CC_EXPORT LayerTreeHostImpl
   const RendererCapabilitiesImpl& GetRendererCapabilities() const;
 
   virtual bool SwapBuffers(const FrameData& frame);
-  void SetNeedsBeginImplFrame(bool enable);
+  void SetNeedsBeginFrame(bool enable);
+  virtual void WillBeginImplFrame(const BeginFrameArgs& args);
   void DidModifyTilePriorities();
 
   void Readback(void* pixels, const gfx::Rect& rect_in_device_viewport);