tabstrip: Use a PaintRecorder to access the Canvas for painting.

ui/compositor/compositing_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_COMPOSITING_RECORDER_H_
 #define UI_COMPOSITOR_COMPOSITING_RECORDER_H_
 
 #include "base/macros.h"
 #include "ui/compositor/compositor_export.h"
 
 namespace gfx {
 class Canvas;
 }
 
 namespace ui {
 class PaintContext;
 
 // A class to provide scoped compositing filters (eg opacity) of painting to a
 // DisplayItemList. The filters provided will be applied to any
 // DisplayItems added to the DisplayItemList while this object is alive. In
 // other words, any nested PaintRecorders or other such Recorders will
 // be filtered by the effect.
 class COMPOSITOR_EXPORT CompositingRecorder {
  public:
-  CompositingRecorder(const PaintContext& context, float opacity);
+  // |alpha| is a value between 0 and 255, where 0 is transparent and 255 is
+  // opaque.
+  CompositingRecorder(const PaintContext& context, int alpha);
   ~CompositingRecorder();
 
  private:
   gfx::Canvas* canvas_;
+  bool saved_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositingRecorder);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_CLIP_TRANSFORM_RECORDER_H_