[#2] Pass gfx structs by const ref (gfx::Rect, gfx::RectF)

cc/layers/scrollbar_theme_painter.h

 // Copyright 2012 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 CC_LAYERS_SCROLLBAR_THEME_PAINTER_H_
 #define CC_LAYERS_SCROLLBAR_THEME_PAINTER_H_
 
 #include "cc/base/cc_export.h"
 
 class SkCanvas;
 
 namespace gfx {
 class Rect;
 }
 
 namespace cc {
 
 class CC_EXPORT ScrollbarThemePainter {
  public:
   virtual ~ScrollbarThemePainter() {}
 
-  virtual void PaintScrollbarBackground(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintTrackBackground(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintBackTrackPart(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintForwardTrackPart(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintBackButtonStart(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintBackButtonEnd(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintForwardButtonStart(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintForwardButtonEnd(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintTickmarks(SkCanvas* canvas, gfx::Rect rect) = 0;
-  virtual void PaintThumb(SkCanvas* canvas, gfx::Rect rect) = 0;
+  virtual void PaintScrollbarBackground(SkCanvas* canvas,
+                                        const gfx::Rect& rect) = 0;
+  virtual void PaintTrackBackground(SkCanvas* canvas,
+                                    const gfx::Rect& rect) = 0;
+  virtual void PaintBackTrackPart(SkCanvas* canvas,
+                                  const gfx::Rect& rect) = 0;
+  virtual void PaintForwardTrackPart(SkCanvas* canvas,
+                                     const gfx::Rect& rect) = 0;
+  virtual void PaintBackButtonStart(SkCanvas* canvas,
+                                    const gfx::Rect& rect) = 0;
+  virtual void PaintBackButtonEnd(SkCanvas* canvas,
+                                  const gfx::Rect& rect) = 0;
+  virtual void PaintForwardButtonStart(SkCanvas* canvas,
+                                       const gfx::Rect& rect) = 0;
+  virtual void PaintForwardButtonEnd(SkCanvas* canvas,
+                                     const gfx::Rect& rect) = 0;
+  virtual void PaintTickmarks(SkCanvas* canvas, const gfx::Rect& rect) = 0;
+  virtual void PaintThumb(SkCanvas* canvas, const gfx::Rect& rect) = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SCROLLBAR_THEME_PAINTER_H_