Use SkBitmap backing instead of GDI backed platform canvas for tiles

cc/resources/bitmap_content_layer_updater.h

 // Copyright 2011 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_RESOURCES_BITMAP_CONTENT_LAYER_UPDATER_H_
 #define CC_RESOURCES_BITMAP_CONTENT_LAYER_UPDATER_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/resources/content_layer_updater.h"
 #include "skia/ext/refptr.h"
+#include "third_party/skia/include/core/SkBitmap.h"
 
 class SkCanvas;
 
 namespace cc {
 
 class LayerPainter;
 class RenderingStatsInstrumenation;
 
 // This class rasterizes the content_rect into a skia bitmap canvas. It then
 // updates textures by copying from the canvas into the texture, using
@@ skipping 37 matching lines @@
   virtual void SetOpaque(bool opaque) OVERRIDE;
   virtual void ReduceMemoryUsage() OVERRIDE;
 
  protected:
   BitmapContentLayerUpdater(
       scoped_ptr<LayerPainter> painter,
       RenderingStatsInstrumentation* stats_instrumenation,
       int layer_id);
   virtual ~BitmapContentLayerUpdater();
 
+  SkBitmap bitmap_backing_;
   skia::RefPtr<SkCanvas> canvas_;
   gfx::Size canvas_size_;
   bool opaque_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BitmapContentLayerUpdater);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_BITMAP_CONTENT_LAYER_UPDATER_H_