[cc] Add and use BeginFrameAck for DidFinishFrame.

content/renderer/gpu/compositor_external_begin_frame_source.h

Index: content/renderer/gpu/compositor_external_begin_frame_source.h
diff --git a/content/renderer/gpu/compositor_external_begin_frame_source.h b/content/renderer/gpu/compositor_external_begin_frame_source.h
index 4b41f2a136f08d5e69762e599d29d73b151f457e..e370827095de4e0134a704a870c12a471389415d 100644
--- a/content/renderer/gpu/compositor_external_begin_frame_source.h
+++ b/content/renderer/gpu/compositor_external_begin_frame_source.h
@@ -43,7 +43,7 @@ class CompositorExternalBeginFrameSource
   void AddObserver(cc::BeginFrameObserver* obs) override;
   void RemoveObserver(cc::BeginFrameObserver* obs) override;
   void DidFinishFrame(cc::BeginFrameObserver* obs,
-                      size_t remaining_frames) override {}
+                      const cc::BeginFrameAck& ack) override {}

[brianderson, 2016/12/21 20:15:06]

Are you planning to implement this in a followup patch?

[Eric Seckler, 2016/12/22 11:11:48]

Yup, together with ack-tracking within ExternalBFS. Added a TODO.

   bool IsThrottled() const override;
 
   // cc::ExternalBeginFrameSourceClient implementation.