Cleanup: Remove some unneeded Extension* class forward declarations.

chrome/browser/extensions/error_console/error_console.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_EXTENSIONS_ERROR_CONSOLE_ERROR_CONSOLE_H_
 #define CHROME_BROWSER_EXTENSIONS_ERROR_CONSOLE_ERROR_CONSOLE_H_
 
 #include <deque>
 #include <map>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "base/prefs/pref_change_registrar.h"
 #include "base/scoped_observer.h"
 #include "base/threading/thread_checker.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "extensions/browser/error_map.h"
 #include "extensions/browser/extension_error.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extension_registry_observer.h"
 
 namespace content {
 class NotificationDetails;
 class NotificationSource;
 class RenderViewHost;
 }
 
-class ExtensionService;
 class Profile;
 
 namespace extensions {
 class Extension;
 class ExtensionPrefs;
 
 // The ErrorConsole is a central object to which all extension errors are
 // reported. This includes errors detected in extensions core, as well as
 // runtime Javascript errors. If FeatureSwitch::error_console() is enabled these
 // errors can be viewed at chrome://extensions in developer mode.
@@ skipping 142 matching lines @@
 
   ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
       registry_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ErrorConsole);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_ERROR_CONSOLE_ERROR_CONSOLE_H_