Replace more ObserverList with base::ObserverList.

extensions/browser/app_window/app_window_registry.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_APP_WINDOW_APP_WINDOW_REGISTRY_H_
 #define EXTENSIONS_BROWSER_APP_WINDOW_APP_WINDOW_REGISTRY_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 120 matching lines @@
   // Otherwise adds |app_window| to the back of |app_windows_|.
   void AddAppWindowToList(AppWindow* app_window);
 
   // Bring |app_window| to the front of |app_windows_|. If it is not in the
   // list, add it first.
   void BringToFront(AppWindow* app_window);
 
   content::BrowserContext* context_;
   AppWindowList app_windows_;
   InspectedWindowSet inspected_windows_;
-  ObserverList<Observer> observers_;
+  base::ObserverList<Observer> observers_;
   base::Callback<void(content::DevToolsAgentHost*, bool)> devtools_callback_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_APP_WINDOW_APP_WINDOW_REGISTRY_H_