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

content/browser/renderer_host/backing_store_skia.cc

-// 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.
 
 #include "content/browser/renderer_host/backing_store_skia.h"
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "skia/ext/platform_canvas.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/canvas_skia.h"
@@ skipping 11 matching lines @@
     : BackingStore(widget, size) {
   bitmap_.setConfig(SkBitmap::kARGB_8888_Config, size.width(), size.height());
   bitmap_.allocPixels();
   canvas_.reset(new SkCanvas(bitmap_));
 }
 
 BackingStoreSkia::~BackingStoreSkia() {
 }
 
 void BackingStoreSkia::SkiaShowRect(const gfx::Point& point,
-                                    gfx::Canvas* canvas) {
+                                    gfx::CanvasSkia* canvas) {
   canvas->GetSkCanvas()->drawBitmap(bitmap_,
       SkIntToScalar(point.x()), SkIntToScalar(point.y()));
 }
 
 size_t BackingStoreSkia::MemorySize() {
   // NOTE: The computation may be different when the canvas is a subrectangle of
   // a larger bitmap.
   return size().GetArea() * 4;
 }
 
@@ skipping 58 matching lines @@
     return false;
 
   SkBitmap bitmap = skia::GetTopDevice(*output)->accessBitmap(true);
   SkIRect skrect = SkIRect::MakeXYWH(rect.x(), rect.y(), width, height);
   SkBitmap b;
   if (!canvas_->readPixels(skrect, &b))
     return false;
   output->writePixels(b, rect.x(), rect.y());
   return true;
 }