Theme suppliers: Avoid all Image copying.

chrome/browser/themes/browser_theme_pack.h

 // Copyright (c) 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 CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 #define CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 66 matching lines @@
   // BuildFromDataPack(). Often (but not always) called from the file thread;
   // implementation should be threadsafe because neither thread will write to
   // |image_memory_| and the worker thread will keep a reference to prevent
   // destruction.
   bool WriteToDisk(const base::FilePath& path) const;
 
   // Overridden from CustomThemeSupplier:
   bool GetTint(int id, color_utils::HSL* hsl) const override;
   bool GetColor(int id, SkColor* color) const override;
   bool GetDisplayProperty(int id, int* result) const override;
-  gfx::Image GetImageNamed(int id) override;
+  const gfx::Image& GetImageNamed(int id) override;
   base::RefCountedMemory* GetRawData(int id, ui::ScaleFactor scale_factor)
       const override;
   bool HasCustomImage(int id) const override;
 
  private:
   friend class BrowserThemePackTest;
 
   // Cached images.
   typedef std::map<int, gfx::Image> ImageCache;
 
@@ skipping 76 matching lines @@
   // in |images|. Must be called after GenerateFrameImages().
   void CreateTabBackgroundImages(ImageCache* images) const;
 
   // Takes all the SkBitmaps in |images|, encodes them as PNGs and places
   // them in |reencoded_images|.
   void RepackImages(const ImageCache& images,
                     RawImages* reencoded_images) const;
 
   // Takes all images in |source| and puts them in |destination|, freeing any
   // image already in |destination| that |source| would overwrite.
-  void MergeImageCaches(const ImageCache& source,
-                        ImageCache* destination) const;
+  void MergeImageCaches(ImageCache source, ImageCache* destination) const;
 
   // Copies images from |source| to |destination| such that the lifetimes of
   // the images in |destination| are not affected by the lifetimes of the
   // images in |source|.
   void CopyImagesTo(const ImageCache& source, ImageCache* destination) const;
 
   // Changes the RefCountedMemory based |images| into StringPiece data in |out|.
   void AddRawImagesTo(const RawImages& images, RawDataForWriting* out) const;
 
   // Retrieves the tint OR the default tint. Unlike the public interface, we
@@ skipping 74 matching lines @@
   // Cache of images created in BuildFromExtension(). Once the theme pack is
   // created, this cache should only be accessed on the file thread. There
   // should be no IDs in |image_memory_| that are in |images_on_file_thread_|
   // or vice versa.
   ImageCache images_on_file_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserThemePack);
 };
 
 #endif  // CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_