cc: Don't pass simple well-defined classes by reference.

cc/resources/picture.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_RESOURCES_PICTURE_H_
 #define CC_RESOURCES_PICTURE_H_
 
 #include <list>
 #include <string>
 #include <vector>
@@ skipping 16 matching lines @@
 class ContentLayerClient;
 struct RenderingStats;
 
 class CC_EXPORT Picture
     : public base::RefCountedThreadSafe<Picture> {
  public:
   static scoped_refptr<Picture> Create(gfx::Rect layer_rect);
   static scoped_refptr<Picture> CreateFromBase64String(
       const std::string& encoded_string);
 
-  const gfx::Rect& LayerRect() const { return layer_rect_; }
-  const gfx::Rect& OpaqueRect() const { return opaque_rect_; }
+  gfx::Rect LayerRect() const { return layer_rect_; }
+  gfx::Rect OpaqueRect() const { return opaque_rect_; }
 
   // Get thread-safe clone for rasterizing with on a specific thread.
   scoped_refptr<Picture> GetCloneForDrawingOnThread(
       unsigned thread_index) const;
 
   // Make thread-safe clones for rasterizing with.
   void CloneForDrawing(int num_threads);
 
   // Record a paint operation. To be able to safely use this SkPicture for
   // playback on a different thread this can only be called once.
   void Record(ContentLayerClient*, RenderingStats*,
       const SkTileGridPicture::TileGridInfo& tile_grid_info);
 
   // Has Record() been called yet?
   bool HasRecording() const { return picture_.get() != NULL; }
 
   // Apply this contents scale and raster the content rect into the canvas.
   void Raster(SkCanvas* canvas,
               gfx::Rect content_rect,
               float contents_scale,
               bool enable_lcd_text);
 
   void GatherPixelRefs(
-      const gfx::Rect& layer_rect,
+      gfx::Rect layer_rect,
       std::list<skia::LazyPixelRef*>& pixel_ref_list);
 
   void AsBase64String(std::string* output) const;
 
  private:
   explicit Picture(gfx::Rect layer_rect);
   Picture(const std::string& encoded_string, bool* success);
   // This constructor assumes SkPicture is already ref'd and transfers
   // ownership to this picture.
   Picture(const skia::RefPtr<SkPicture>&,
           gfx::Rect layer_rect,
           gfx::Rect opaque_rect);
   ~Picture();
 
   gfx::Rect layer_rect_;
   gfx::Rect opaque_rect_;
   skia::RefPtr<SkPicture> picture_;
 
   typedef std::vector<scoped_refptr<Picture> > PictureVector;
   PictureVector clones_;
 
   friend class base::RefCountedThreadSafe<Picture>;
   DISALLOW_COPY_AND_ASSIGN(Picture);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_H_