ui: Eliminate allocating gfx::Canvas on the heap for every view.

ui/compositor/paint_recorder.h

 // Copyright 2015 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.
 
 #ifndef UI_COMPOSITOR_PAINT_RECORDER_H_
 #define UI_COMPOSITOR_PAINT_RECORDER_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "skia/ext/refptr.h"
 #include "ui/compositor/compositor_export.h"
+#include "ui/gfx/canvas.h"
 
 namespace cc {
 class DisplayItemList;
 }
 
 namespace gfx {
 class Canvas;
 }
 
 class SkCanvas;
@@ skipping 13 matching lines @@
   // PaintRecorder is in use.
   PaintRecorder(const PaintContext& context, PaintCache* cache);
   explicit PaintRecorder(const PaintContext& context);
   ~PaintRecorder();
 
   // Gets a gfx::Canvas for painting into.
   gfx::Canvas* canvas() { return canvas_; }
 
  private:
   const PaintContext& context_;
+  gfx::Canvas owned_canvas_;
   gfx::Canvas* canvas_;
-  scoped_ptr<gfx::Canvas> owned_canvas_;
   PaintCache* cache_;
 
   DISALLOW_COPY_AND_ASSIGN(PaintRecorder);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_PAINT_RECORDER_H_