Theme suppliers: Avoid all Image copying.

chrome/browser/themes/custom_theme_supplier.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 CHROME_BROWSER_THEMES_CUSTOM_THEME_SUPPLIER_H_
 #define CHROME_BROWSER_THEMES_CUSTOM_THEME_SUPPLIER_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "content/public/browser/browser_thread.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/layout.h"
+#include "ui/gfx/image/image.h"
 
 namespace base {
 class RefCountedMemory;
 }
 
 namespace color_utils {
 struct HSL;
 }
 
 namespace gfx {
@@ skipping 27 matching lines @@
   // If the theme specifies data for the corresponding |id|, returns true and
   // writes the corresponding value to the output parameter. These methods
   // should not return the default data. These methods should only be called
   // from the UI thread.
   virtual bool GetTint(int id, color_utils::HSL* hsl) const;
   virtual bool GetColor(int id, SkColor* color) const;
   virtual bool GetDisplayProperty(int id, int* result) const;
 
   // Returns the theme image for |id|. Returns an empty image if no image is
   // found for |id|.
-  virtual gfx::Image GetImageNamed(int id);
+  virtual const gfx::Image& GetImageNamed(int id);
 
   // Returns the raw PNG encoded data for IDR_THEME_NTP_*. This method only
   // works for the NTP attribution and background resources.
   virtual base::RefCountedMemory* GetRawData(
       int id, ui::ScaleFactor scale_factor) const;
 
   // Whether this theme provides an image for |id|.
   virtual bool HasCustomImage(int id) const;
 
  protected:
   virtual ~CustomThemeSupplier();
 
+  const gfx::Image& empty_image() const { return empty_image_; }
+
  private:
   friend struct content::BrowserThread::DeleteOnThread<
       content::BrowserThread::FILE>;
   friend class base::DeleteHelper<CustomThemeSupplier>;
 
   ThemeType theme_type_;
 
+  gfx::Image empty_image_;
+
   DISALLOW_COPY_AND_ASSIGN(CustomThemeSupplier);
 };
 
 #endif  // CHROME_BROWSER_THEMES_CUSTOM_THEME_SUPPLIER_H_