[cc] CompositorFrameSinkSupport: Defer BeginFrameAck of pending frames.

cc/surfaces/compositor_frame_sink_support.h

Index: cc/surfaces/compositor_frame_sink_support.h
diff --git a/cc/surfaces/compositor_frame_sink_support.h b/cc/surfaces/compositor_frame_sink_support.h
index bdafb4933e6c0f752edc1fde38a9d63fd003d6b5..cf17c4e75a7fbc1e7b56c1f0dd3c21eb466d0895 100644
--- a/cc/surfaces/compositor_frame_sink_support.h
+++ b/cc/surfaces/compositor_frame_sink_support.h
@@ -68,6 +68,7 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void RemoveTopLevelRootReference(const SurfaceId& surface_id);
 
   void DidReceiveCompositorFrameAck();
+  void PendingFrameDiscarded();
 
   // SurfaceFactoryClient implementation.
   void ReferencedSurfacesChanged(
@@ -78,6 +79,7 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void SetBeginFrameSource(BeginFrameSource* begin_frame_source) override;
   void WillDrawSurface(const LocalSurfaceId& local_surface_id,
                        const gfx::Rect& damage_rect) override;
+  void PendingFrameActivated(const LocalSurfaceId& local_surface_id) override;
 
   // BeginFrameObserver implementation.
   void OnBeginFrame(const BeginFrameArgs& args) override;
@@ -85,6 +87,8 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void OnBeginFrameSourcePausedChanged(bool paused) override;
 
   void UpdateNeedsBeginFramesInternal();
+  void AcknowledgeBeginFrame(const BeginFrameAck& ack);
+  void AcknowledgeLastBeginFrameWithoutUpdates();
 
   CompositorFrameSinkSupportClient* const client_;
 
@@ -98,14 +102,28 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   int ack_pending_count_ = 0;
   ReturnedResourceArray surface_returned_resources_;
 
+  // Whether a CompositorFrame is currently pending to be activated.
+  bool has_pending_frame_ = false;
+
   // The begin frame source being observered. Null if none.
   BeginFrameSource* begin_frame_source_ = nullptr;
 
   // The last begin frame args generated by the begin frame source.
   BeginFrameArgs last_begin_frame_args_;
 
+  // The BeginFrameAck that will be issued when the last submitted
+  // CompositorFrame is activated.
+  BeginFrameAck begin_frame_ack_for_pending_frame_;
+
+  // Whether the last BeginFrame was forwarded to the client.
+  bool last_begin_frame_sent_to_client_ = true;
+
+  uint32_t latest_confirmed_begin_frame_source_id_ = 0;
+  uint64_t latest_confirmed_begin_frame_sequence_number_ =
+      BeginFrameArgs::kInvalidFrameNumber;
+
   // Whether a request for begin frames has been issued.
-  bool needs_begin_frame_ = false;
+  bool client_needs_begin_frame_ = false;
 
   // Whether or not a frame observer has been added.
   bool added_frame_observer_ = false;