cc: Make LayerTreeHostImpl::SwapBuffers not virtual.

cc/output/output_surface_client.h

 // Copyright 2012 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.
 
 #ifndef CC_OUTPUT_OUTPUT_SURFACE_CLIENT_H_
 #define CC_OUTPUT_OUTPUT_SURFACE_CLIENT_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
@@ skipping 16 matching lines @@
  public:
   // TODO(enne): Remove this in favor of using SetBeginFrameSource.
   virtual void CommitVSyncParameters(base::TimeTicks timebase,
                                      base::TimeDelta interval) = 0;
   // Pass the begin frame source for the client to observe.  Client does not own
   // the BeginFrameSource.  OutputSurface should call this once after binding to
   // the client and then call again with a null while detaching.
   virtual void SetBeginFrameSource(BeginFrameSource* source) = 0;
 
   virtual void SetNeedsRedrawRect(const gfx::Rect& damage_rect) = 0;
+  // For LayerTreeHostImpl, this is more of a OnSwapBuffersAck from the display
+  // compositor that it received and will use the frame, unblocking it from
+  // producing more frames.
+  // For the display compositor this is literally a notification that the swap
+  // to the hardware is complete.
   virtual void DidSwapBuffersComplete() = 0;
   virtual void DidReceiveTextureInUseResponses(
       const gpu::TextureInUseResponses& responses) = 0;
   virtual void ReclaimResources(const CompositorFrameAck* ack) = 0;
   virtual void DidLoseOutputSurface() = 0;
   virtual void SetExternalTilePriorityConstraints(
       const gfx::Rect& viewport_rect,
       const gfx::Transform& transform) = 0;
   virtual void SetMemoryPolicy(const ManagedMemoryPolicy& policy) = 0;
   // If set, |callback| will be called subsequent to each new tree activation,
   // regardless of the compositor visibility or damage. |callback| must remain
   // valid for the lifetime of the OutputSurfaceClient or until unregisted --
   // use SetTreeActivationCallback(base::Closure()) to unregister it.
   virtual void SetTreeActivationCallback(const base::Closure& callback) = 0;
   // This allows the output surface to ask its client for a draw.
   virtual void OnDraw(const gfx::Transform& transform,
                       const gfx::Rect& viewport,
                       const gfx::Rect& clip,
                       bool resourceless_software_draw) = 0;
 
  protected:
   virtual ~OutputSurfaceClient() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_OUTPUT_SURFACE_CLIENT_H_