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

ui/views/controls/button/image_button.cc

Index: ui/views/controls/button/image_button.cc
diff --git a/ui/views/controls/button/image_button.cc b/ui/views/controls/button/image_button.cc
index 4bf214ab02123763720f79d1189a818e66465d34..730de1942c9c879f001c2b95f6c126e99686d64a 100644
--- a/ui/views/controls/button/image_button.cc
+++ b/ui/views/controls/button/image_button.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -64,7 +64,7 @@ gfx::Size ImageButton::GetPreferredSize() {
   return preferred_size_;
 }
 
-void ImageButton::OnPaint(gfx::Canvas* canvas) {
+void ImageButton::OnPaint(gfx::CanvasSkia* canvas) {
   // Call the base class first to paint any background/borders.
   View::OnPaint(canvas);