Theme suppliers: Avoid all Image copying.

chrome/browser/themes/theme_service.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_THEME_SERVICE_H_
 #define CHROME_BROWSER_THEMES_THEME_SERVICE_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 231 matching lines @@
   bool HasCustomColor(int id) const;
   NSColor* GetNSColor(int id, bool incognito) const;
   NSColor* GetNSColorTint(int id) const;
   NSGradient* GetNSGradient(int id) const;
 #endif
 
   // Returns a cross platform image for an id.
   //
   // TODO(erg): Make this part of the ui::ThemeProvider and the main way to get
   // theme properties out of the theme provider since it's cross platform.
-  gfx::Image GetImageNamed(int id, bool incognito) const;
+  const gfx::Image& GetImageNamed(int id, bool incognito) const;
 
   // Called when the extension service is ready.
   void OnExtensionServiceReady();
 
   // Migrate the theme to the new theme pack schema by recreating the data pack
   // from the extension.
   void MigrateTheme();
 
   // Replaces the current theme supplier with a new one and calls
   // StopUsingTheme() or StartUsingTheme() as appropriate.
@@ skipping 61 matching lines @@
 
   BrowserThemeProvider original_theme_provider_;
   BrowserThemeProvider incognito_theme_provider_;
 
   base::WeakPtrFactory<ThemeService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThemeService);
 };
 
 #endif  // CHROME_BROWSER_THEMES_THEME_SERVICE_H_