[cc] Acknowledge BeginFrames in SurfaceDependencyTracker.

cc/surfaces/compositor_frame_sink_support.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/surfaces/compositor_frame_sink_support.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "cc/output/compositor_frame.h"
@@ skipping 51 matching lines @@
   surface_factory_.EvictSurface();
 }
 
 void CompositorFrameSinkSupport::SetNeedsBeginFrame(bool needs_begin_frame) {
   needs_begin_frame_ = needs_begin_frame;
   UpdateNeedsBeginFramesInternal();
 }
 
 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;
   }
 
   // |has_damage| is not transmitted, but false by default.
   DCHECK(!ack.has_damage);
   if (begin_frame_source_)
     begin_frame_source_->DidFinishFrame(this, ack);
 }
@@ skipping 12 matching lines @@
   }
   // |has_damage| is not transmitted.
   frame.metadata.begin_frame_ack.has_damage = true;
 
   BeginFrameAck ack = frame.metadata.begin_frame_ack;
   surface_factory_.SubmitCompositorFrame(
       local_surface_id, std::move(frame),
       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);
 }
 
 void CompositorFrameSinkSupport::UpdateSurfaceReferences(
     const SurfaceId& last_surface_id,
     const LocalSurfaceId& local_surface_id) {
   const bool surface_id_changed =
       last_surface_id.local_surface_id() != local_surface_id;
 
@@ skipping 139 matching lines @@
   else
     begin_frame_source_->RemoveObserver(this);
 }
 
 void CompositorFrameSinkSupport::RequestCopyOfSurface(
     std::unique_ptr<CopyOutputRequest> request) {
   surface_factory_.RequestCopyOfSurface(std::move(request));
 }
 
 }  // namespace cc