[cc] Pass on BeginFrameAcks from CompositorEBFS through RWHVAura, DFH.

content/renderer/gpu/compositor_external_begin_frame_source.cc

Index: content/renderer/gpu/compositor_external_begin_frame_source.cc
diff --git a/content/renderer/gpu/compositor_external_begin_frame_source.cc b/content/renderer/gpu/compositor_external_begin_frame_source.cc
index 90f5554ba3915d1deb71674f38f7eaaed7716598..4c1608158b3c2d6f16de7fea4befde456b3b9b55 100644
--- a/content/renderer/gpu/compositor_external_begin_frame_source.cc
+++ b/content/renderer/gpu/compositor_external_begin_frame_source.cc
@@ -55,6 +55,12 @@ void CompositorExternalBeginFrameSource::RemoveObserver(
   external_begin_frame_source_.RemoveObserver(obs);
 }
 
+void CompositorExternalBeginFrameSource::DidFinishFrame(
+    cc::BeginFrameObserver* obs,
+    const cc::BeginFrameAck& ack) {
+  external_begin_frame_source_.DidFinishFrame(obs, ack);
+}
+
 bool CompositorExternalBeginFrameSource::IsThrottled() const {
   return true;
 }
@@ -66,7 +72,10 @@ void CompositorExternalBeginFrameSource::OnNeedsBeginFrames(
 
 void CompositorExternalBeginFrameSource::OnDidFinishFrame(
     const cc::BeginFrameAck& ack) {
-  // TODO(eseckler): Pass on the ack to the view host.
+  DCHECK_LE(cc::BeginFrameArgs::kStartingFrameNumber, ack.sequence_number);
+  // If there was damage, ViewHostMsg_SwapCompositorFrame includes the ack.
+  if (!ack.has_damage)
+    Send(new ViewHostMsg_BeginFrameDidNotSwap(routing_id_, ack));
 }
 
 void CompositorExternalBeginFrameSource::OnMessageReceived(