ui/gfx: Make gfx::Canvas inherit from gfx::CanvasSkia.

ui/gfx/compositor/layer_unittest.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 "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/path_service.h"
@@ skipping 208 matching lines @@
 
   void AddColor(SkColor color) {
     colors_.push_back(color);
   }
 
   gfx::Size paint_size() const { return paint_size_; }
   int color_index() const { return color_index_; }
 
   // Overridden from LayerDelegate:
   virtual void OnPaintLayer(gfx::Canvas* canvas) OVERRIDE {
-    SkBitmap contents = canvas->AsCanvasSkia()->ExtractBitmap();
+    SkBitmap contents = canvas->ExtractBitmap();
     paint_size_ = gfx::Size(contents.width(), contents.height());
     canvas->FillRect(gfx::Rect(paint_size_), colors_[color_index_]);
     color_index_ = (color_index_ + 1) % static_cast<int>(colors_.size());
   }
 
  private:
   std::vector<SkColor> colors_;
   int color_index_;
   gfx::Size paint_size_;
 
@@ skipping 774 matching lines @@
   EXPECT_TRUE(schedule_draw_invoked_);
   // Because SchedulePaint() was invoked from OnPaintLayer() |child| should
   // still need to be painted.
   DrawTree(root.get());
   EXPECT_EQ(1, child_delegate.GetPaintCountAndClear());
   EXPECT_TRUE(child_delegate.last_clip_rect().Contains(
                   gfx::Rect(10, 10, 30, 30)));
 }
 
 } // namespace ui