Refactor the PlatformContext layer to have only one class.

webkit/tools/test_shell/mac/webwidget_host.mm

 // Copyright (c) 2008 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.
 
 #import <Cocoa/Cocoa.h>
 
 #include "webkit/tools/test_shell/webwidget_host.h"
 
-#include "base/gfx/platform_canvas_mac.h"
+#include "base/gfx/platform_canvas.h"
 #include "base/gfx/rect.h"
 #include "base/gfx/size.h"
 #include "base/logging.h"
 #include "webkit/api/public/mac/WebInputEventFactory.h"
 #include "webkit/api/public/mac/WebScreenInfoFactory.h"
 #include "webkit/api/public/WebInputEvent.h"
 #include "webkit/api/public/WebScreenInfo.h"
 #include "webkit/api/public/WebSize.h"
 #include "webkit/glue/webwidget.h"
 #include "webkit/tools/test_shell/test_shell.h"
@@ skipping 257 matching lines @@
 void WebWidgetHost::PaintRect(const gfx::Rect& rect) {
 #ifndef NDEBUG
   DCHECK(!painting_);
 #endif
   DCHECK(canvas_.get());
 
   set_painting(true);
   webwidget_->Paint(canvas_.get(), rect);
   set_painting(false);
 }