[cc] Acknowledge BeginFrames in SurfaceDependencyTracker.

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 b0d7dc28df3399d40605455d89aabe40abf9d80e..0443c4bd3b7337be2ad0925f7e22a70e95de14c5 100644
--- a/cc/surfaces/compositor_frame_sink_support.cc
+++ b/cc/surfaces/compositor_frame_sink_support.cc
@@ -69,9 +69,6 @@ void CompositorFrameSinkSupport::SetNeedsBeginFrame(bool needs_begin_frame) {
 
 void CompositorFrameSinkSupport::BeginFrameDidNotSwap(
     const BeginFrameAck& ack) {
-  // TODO(eseckler): While a pending CompositorFrame exists (see TODO below), we
-  // should not acknowledge immediately. Instead, we should update the ack that
-  // will be sent to DisplayScheduler when the pending frame is activated.
   if (ack.sequence_number < BeginFrameArgs::kStartingFrameNumber) {
     DLOG(ERROR) << "Received BeginFrameDidNotSwap with invalid BeginFrameAck.";
     return;
@@ -104,11 +101,6 @@ void CompositorFrameSinkSupport::SubmitCompositorFrame(
       base::Bind(&CompositorFrameSinkSupport::DidReceiveCompositorFrameAck,
                  weak_factory_.GetWeakPtr()));
 
-  // TODO(eseckler): The CompositorFrame submitted below might not be activated
-  // right away b/c of surface synchronization. We should only send the
-  // BeginFrameAck to DisplayScheduler when it is activated. This also means
-  // that we need to stay an active BFO while a CompositorFrame is pending.
-  // See https://crbug.com/703079.
   if (begin_frame_source_)
     begin_frame_source_->DidFinishFrame(this, ack);
 }