Refactor the PlatformContext layer to have only one class.

views/widget/root_view_gtk.cc

 // Copyright (c) 2006-2008 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.
 
 #include "views/widget/root_view.h"
 
 #include <gtk/gtk.h>
 
-#include "app/gfx/canvas.h"
+#include "app/gfx/canvas_paint.h"
 #include "base/logging.h"
 #include "views/widget/widget_gtk.h"
 
 namespace views {
 
 void RootView::OnPaint(GdkEventExpose* event) {
   gfx::CanvasPaint canvas(event);
 
-  if (!canvas.isEmpty()) {
+  if (!canvas.is_empty()) {
     canvas.set_composite_alpha(
         static_cast<WidgetGtk*>(GetWidget())->is_transparent());
     SchedulePaint(gfx::Rect(canvas.rectangle()), false);
     if (NeedsPainting(false)) {
       ProcessPaint(&canvas);
     }
   }
 }
 
 }