Refactor the PlatformContext layer to have only one class.

views/controls/tree/tree_view.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/controls/tree/tree_view.h"
 
 #include <atlbase.h>
 #include <atlapp.h>
 #include <atlmisc.h>
 
-#include "app/gfx/canvas.h"
+#include "app/gfx/canvas_paint.h"
 #include "app/gfx/icon_util.h"
 #include "app/l10n_util.h"
 #include "app/l10n_util_win.h"
 #include "app/resource_bundle.h"
 #include "base/stl_util-inl.h"
 #include "base/win_util.h"
 #include "grit/app_resources.h"
 #include "views/focus/focus_manager.h"
 #include "views/widget/widget.h"
 
@@ skipping 716 matching lines @@
       }
       // Fall through and let the default handler process as well.
       break;
   }
   WNDPROC handler = tree->original_handler_;
   DCHECK(handler);
   return CallWindowProc(handler, window, message, w_param, l_param);
 }
 
 }  // namespace views