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

cc/test/fake_scrollbar.cc

 // 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.
 
 #include "cc/test/fake_scrollbar.h"
 
 #include "third_party/skia/include/core/SkCanvas.h"
 
 namespace cc {
 
@@ skipping 38 matching lines @@
 int FakeScrollbar::ThumbLength() const {
   return thumb_length_;
 }
 
 gfx::Rect FakeScrollbar::TrackRect() const {
   return track_rect_;
 }
 
 void FakeScrollbar::PaintPart(SkCanvas* canvas,
                              ScrollbarPart part,
-                             gfx::Rect content_rect) {
+                             const gfx::Rect& content_rect) {
   if (!paint_)
     return;
 
   // Fill the scrollbar with a different color each time.
   fill_color_++;
   canvas->clear(SK_ColorBLACK | fill_color_);
 }
 
 }  // namespace cc