Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

chrome/renderer/automation/automation_renderer_helper.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 "chrome/renderer/automation/automation_renderer_helper.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/json/json_writer.h"
@@ skipping 49 matching lines @@
   bool fixed_layout_enabled = view->isFixedLayoutModeEnabled();
   WebSize fixed_size = view->fixedLayoutSize();
 
   frame->setCanHaveScrollbars(false);
   view->setFixedLayoutSize(old_size);
   view->enableFixedLayoutMode(true);
   view->resize(new_size);
   view->layout();
   frame->setScrollOffset(WebSize(0, 0));
 
-  skia::PlatformCanvas canvas(
-      new_size.width, new_size.height, true /* is_opaque */);
-  view->paint(webkit_glue::ToWebCanvas(&canvas),
+  skia::ScopedPlatformCanvas canvas(new_size.width, new_size.height, true);
+
+  view->paint(webkit_glue::ToWebCanvas(canvas),
               gfx::Rect(0, 0, new_size.width, new_size.height));
 
   frame->setCanHaveScrollbars(true);
   view->setFixedLayoutSize(fixed_size);
   view->enableFixedLayoutMode(fixed_layout_enabled);
   view->resize(old_size);
   view->layout();
   frame->setScrollOffset(WebSize(old_scroll.width - min_scroll.width,
                                  old_scroll.height - min_scroll.height));
 
-  const SkBitmap& bmp = skia::GetTopDevice(canvas)->accessBitmap(false);
+  const SkBitmap& bmp = skia::GetTopDevice(*canvas)->accessBitmap(false);
   SkAutoLockPixels lock_pixels(bmp);
   // EncodeBGRA uses FORMAT_SkBitmap, which doesn't work on windows for some
   // cases dealing with transparency. See crbug.com/96317. Use FORMAT_BGRA.
   bool encode_success = gfx::PNGCodec::Encode(
       reinterpret_cast<unsigned char*>(bmp.getPixels()),
       gfx::PNGCodec::FORMAT_BGRA,
       gfx::Size(bmp.width(), bmp.height()),
       bmp.rowBytes(),
       true,  // discard_transparency
       std::vector<gfx::PNGCodec::Comment>(),
@@ skipping 187 matching lines @@
       routing_id(), frame->identifier()));
 }
 
 void AutomationRendererHelper::OnProcessMouseEvent(
     const AutomationMouseEvent& event) {
   std::string error_msg;
   bool success = ProcessMouseEvent(event, &error_msg);
   Send(new AutomationMsg_ProcessMouseEventACK(
       routing_id(), success, error_msg));
 }