Ensure alpha channel in backbuffer is correct with DirectComposition.

ui/gl/gl_surface.cc

 // Copyright (c) 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.
 
 #include "ui/gl/gl_surface.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 205 matching lines @@
 }
 
 bool GLSurface::IsSurfaceless() const {
   return false;
 }
 
 bool GLSurface::FlipsVertically() const {
   return false;
 }
 
+bool GLSurface::BuffersFlipped() const {
+  return false;
+}
+
 GLSurface* GLSurface::GetCurrent() {
   return current_surface_.Pointer()->Get();
 }
 
 GLSurface::~GLSurface() {
   if (GetCurrent() == this)
     SetCurrent(NULL);
 }
 
 void GLSurface::SetCurrent(GLSurface* surface) {
@@ skipping 144 matching lines @@
 }
 
 bool GLSurfaceAdapter::IsSurfaceless() const {
   return surface_->IsSurfaceless();
 }
 
 bool GLSurfaceAdapter::FlipsVertically() const {
   return surface_->FlipsVertically();
 }
 
+bool GLSurfaceAdapter::BuffersFlipped() const {
+  return surface_->BuffersFlipped();
+}
+
 GLSurfaceAdapter::~GLSurfaceAdapter() {}
 
 }  // namespace gfx