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

cc/layers/scrollbar_layer_impl_base.h

 // Copyright 2013 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_LAYER_IMPL_BASE_H_
 #define CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar.h"
 #include "cc/layers/layer_impl.h"
@@ skipping 35 matching lines @@
   }
   void SetThumbThicknessScaleFactor(float thumb_thickness_scale_factor);
 
  protected:
   ScrollbarLayerImplBase(LayerTreeImpl* tree_impl,
                          int id,
                          ScrollbarOrientation orientation,
                          bool is_left_side_vertical_scrollbar);
   virtual ~ScrollbarLayerImplBase() {}
 
-  gfx::Rect ScrollbarLayerRectToContentRect(gfx::RectF layer_rect) const;
+  gfx::Rect ScrollbarLayerRectToContentRect(const gfx::RectF& layer_rect) const;
 
   float visible_to_total_length_ratio() const {
     return visible_to_total_length_ratio_;
   }
   float vertical_adjust() const { return vertical_adjust_; }
 
   virtual int ThumbThickness() const = 0;
   virtual int ThumbLength() const = 0;
   virtual float TrackLength() const = 0;
   virtual int TrackStart() const = 0;
@@ skipping 16 matching lines @@
   float vertical_adjust_;
 
   float visible_to_total_length_ratio_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarLayerImplBase);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_