cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/surfaces/compositor_frame_sink_support.cc

Index: cc/surfaces/compositor_frame_sink_support.cc
diff --git a/cc/surfaces/compositor_frame_sink_support.cc b/cc/surfaces/compositor_frame_sink_support.cc
index d28ea4a2d4f536c041f515d37c2f613847f5d114..6631dbbbcb6486c43c1308f6cc588e6c9643d41e 100644
--- a/cc/surfaces/compositor_frame_sink_support.cc
+++ b/cc/surfaces/compositor_frame_sink_support.cc
@@ -73,7 +73,12 @@ void CompositorFrameSinkSupport::SubmitCompositorFrame(
       display_->Resize(frame_size);
     }
   }
+
+  uint64_t begin_frame_source_id = frame.metadata.begin_frame_source_id;
+  uint64_t begin_frame_number = frame.metadata.begin_frame_number;
+  uint64_t latest_confirmed_frame = frame.metadata.latest_confirmed_frame;
   ++ack_pending_count_;
+
   surface_factory_.SubmitCompositorFrame(
       local_frame_id_, std::move(frame),
       base::Bind(&CompositorFrameSinkSupport::DidReceiveCompositorFrameAck,
@@ -82,6 +87,17 @@ void CompositorFrameSinkSupport::SubmitCompositorFrame(
     display_->SetLocalFrameId(local_frame_id_,
                               frame.metadata.device_scale_factor);
   }
+
+  BeginFrameAck ack(begin_frame_source_id, begin_frame_number,
+                    latest_confirmed_frame, 0, true);
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);
+}
+
+void CompositorFrameSinkSupport::BeginFrameDidNotDraw(
+    const BeginFrameAck& ack) {
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);
 }
 
 void CompositorFrameSinkSupport::Require(const LocalFrameId& local_frame_id,