[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..26b398fa53be44009ce125e02d04704ad25b6ec7 100644
--- a/cc/surfaces/compositor_frame_sink_support.h
+++ b/cc/surfaces/compositor_frame_sink_support.h
@@ -11,6 +11,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
+#include "base/optional.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/surfaces/referenced_surface_tracker.h"
@@ -56,6 +57,11 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void ForceReclaimResources();
   void ClaimTemporaryReference(const SurfaceId& surface_id);
 
+  base::Optional<BeginFrameAck> begin_frame_ack_for_pending_frame_for_testing()
+      const {
+    return begin_frame_ack_for_pending_frame_;
+  }
+
  private:
   // Update surface references with SurfaceManager for current CompositorFrame
   // that has |local_surface_id|. UpdateReferences() must be called on
@@ -68,6 +74,7 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void RemoveTopLevelRootReference(const SurfaceId& surface_id);
 
   void DidReceiveCompositorFrameAck();
+  void PendingFrameDiscarded();
 
   // SurfaceFactoryClient implementation.
   void ReferencedSurfacesChanged(
@@ -78,6 +85,8 @@ 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;
+  void SurfaceDiscarded(const LocalSurfaceId& local_surface_id) override;
 
   // BeginFrameObserver implementation.
   void OnBeginFrame(const BeginFrameArgs& args) override;
@@ -85,6 +94,13 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void OnBeginFrameSourcePausedChanged(bool paused) override;
 
   void UpdateNeedsBeginFramesInternal();
+  // Send |ack| to BeginFrameSource and update
+  // |latest_confirmed_begin_frame_sequence_number_ / source_id_|.
+  void AcknowledgeBeginFrame(const BeginFrameAck& ack);
+  // Send a no-damage BeginFrameAck for the last BeginFrame that re-confirms the
+  // |latest_confirmed_begin_frame_sequence_number_|. Used to confirm past
+  // BeginFrames while a pending CompositorFrame is queued but not activated.
+  void AcknowledgeLastBeginFrameWithoutUpdates();
 
   CompositorFrameSinkSupportClient* const client_;
 
@@ -104,8 +120,24 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   // 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. Only set if we recently submitted a
+  // CompositorFrame that has not been activated yet.
+  base::Optional<BeginFrameAck> begin_frame_ack_for_pending_frame_;
+  // The surface that the last CompositorFrame was submitted to. Used to
+  // determine whether the last CompositorFrame may have been dropped during
+  // SurfaceDiscarded.
+  LocalSurfaceId surface_id_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;