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

ui/compositor/compositing_recorder.h

Index: ui/compositor/compositing_recorder.h
diff --git a/ui/compositor/compositing_recorder.h b/ui/compositor/compositing_recorder.h
index cd8bcd7a88f39b970e2527410f724890300d584a..1cea558229e762a22ff3828e9ac963f827fa02d4 100644
--- a/ui/compositor/compositing_recorder.h
+++ b/ui/compositor/compositing_recorder.h
@@ -22,11 +22,14 @@ class PaintContext;
 // 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);
 };