chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/pending_extension_manager.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 CHROME_BROWSER_EXTENSIONS_PENDING_EXTENSION_MANAGER_H_
 #define CHROME_BROWSER_EXTENSIONS_PENDING_EXTENSION_MANAGER_H_
 
 #include <list>
 #include <map>
 #include <string>
@@ skipping 12 matching lines @@
 }
 
 namespace content {
 class BrowserContext;
 }
 
 FORWARD_DECLARE_TEST(ExtensionServiceTest,
                      UpdatePendingExtensionAlreadyInstalled);
 
 namespace extensions {
-class Extension;
 class PendingExtensionManager;
 
 class ExtensionUpdaterTest;
 void SetupPendingExtensionManagerForTest(
     int count, const GURL& update_url,
     PendingExtensionManager* pending_extension_manager);
 
 // Class PendingExtensionManager manages the set of extensions which are
 // being installed or updated. In general, installation and updates take
 // time, because they involve downloading, unpacking, and installing.
@@ skipping 116 matching lines @@
   friend void SetupPendingExtensionManagerForTest(
       int count, const GURL& update_url,
       PendingExtensionManager* pending_extension_manager);
 
   DISALLOW_COPY_AND_ASSIGN(PendingExtensionManager);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_PENDING_EXTENSION_MANAGER_H_