[Extensions] Cache extension action icons

chrome/browser/extensions/extension_action_icon_factory.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_EXTENSIONS_EXTENSION_ACTION_ICON_FACTORY_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_ACTION_ICON_FACTORY_H_
 
 #include "base/memory/scoped_ptr.h"
+#include "base/scoped_observer.h"
 #include "extensions/browser/extension_icon_image.h"
 
 class ExtensionAction;
 class ExtensionIconSet;
 class Profile;
 
 namespace extensions {
 class Extension;
 }
 
 // Used to get an icon to be used in the UI for an extension action.
 // If the extension action icon is the default icon defined in the extension's
 // manifest, it is loaded using extensions::IconImage. This icon can be loaded
 // asynchronously. The factory observes underlying IconImage and notifies its
 // own observer when the icon image changes.
 class ExtensionActionIconFactory : public extensions::IconImage::Observer {
  public:
   class Observer {
    public:
     virtual ~Observer() {}
     // Called when the underlying icon image changes.
     virtual void OnIconUpdated() = 0;
   };
 
   // Observer should outlive this.
   ExtensionActionIconFactory(Profile* profile,
                              const extensions::Extension* extension,
-                             const ExtensionAction* action,
+                             ExtensionAction* action,
                              Observer* observer);
   ~ExtensionActionIconFactory() override;
 
   // extensions::IconImage override.
   void OnExtensionIconImageChanged(extensions::IconImage* image) override;
+  void OnExtensionIconImageDestroyed(extensions::IconImage* image) override;
 
   // Gets the extension action icon for the tab.
   // If there is an icon set using |SetIcon|, that icon is returned.
   // Else, if there is a default icon set for the extension action, the icon is
   // created using IconImage. Observer is triggered wheniever the icon gets
   // updated.
   // Else, extension favicon is returned.
   // In all cases, action's attention and animation icon transformations are
   // applied on the icon.
   gfx::Image GetIcon(int tab_id);
 
  private:
   // Gets the icon that should be returned by |GetIcon| (without the attention
   // and animation transformations).
   gfx::ImageSkia GetBaseIconFromAction(int tab_id);
 
   const extensions::Extension* extension_;
   const ExtensionAction* action_;
   Observer* observer_;
-  // Underlying icon image for the default icon.
-  scoped_ptr<extensions::IconImage> default_icon_;
+
+  ScopedObserver<extensions::IconImage, extensions::IconImage::Observer>
+      icon_image_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionActionIconFactory);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_ACTION_ICON_FACTORY_H_