[cc] Plumb BeginFrameAcks through SurfaceManager to DisplayScheduler.

content/browser/frame_host/render_widget_host_view_child_frame_unittest.cc

 // Copyright 2014 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 "content/browser/frame_host/render_widget_host_view_child_frame.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 226 matching lines @@
 
   // Submit another frame with the same local surface id. The same id should be
   // usable.
   view_->SubmitCompositorFrame(
       kArbitraryLocalSurfaceId,
       CreateDelegatedFrame(scale_factor, view_size, view_rect));
   EXPECT_EQ(kArbitraryLocalSurfaceId, GetLocalSurfaceId());
   EXPECT_TRUE(view_->has_frame());
 }
 
-// TODO(eseckler): Add back tests for BeginFrameAck forwarding through
-// RenderWidgetHostViewChildFrame and CompositorFrameSinkSupport when we add
-// plumbing of BeginFrameAcks through SurfaceObservers.
-
 }  // namespace content