chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/api/signed_in_devices/signed_in_devices_manager.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_API_SIGNED_IN_DEVICES_SIGNED_IN_DEVICES_MANAGER_H__
 #define CHROME_BROWSER_EXTENSIONS_API_SIGNED_IN_DEVICES_SIGNED_IN_DEVICES_MANAGER_H__
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/scoped_observer.h"
 #include "components/sync/device_info/device_info_tracker.h"
 #include "extensions/browser/browser_context_keyed_api_factory.h"
 #include "extensions/browser/event_router.h"
 #include "extensions/browser/extension_registry_observer.h"
 
 class Profile;
 
 namespace content {
 class BrowserContext;
-class NotificationDetails;
-class NotificationObserver;
 class NotificationRegistrar;
 }  // namespace content
 
 namespace extensions {
 class BrowserContextKeyedAPI;
 class ExtensionRegistry;
 
 struct EventListenerInfo;
 
 // An object of this class is created for each extension that has registered
@@ skipping 63 matching lines @@
       extension_registry_observer_;
 
   FRIEND_TEST_ALL_PREFIXES(SignedInDevicesManager, UpdateListener);
 
   DISALLOW_COPY_AND_ASSIGN(SignedInDevicesManager);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_SIGNED_IN_DEVICES_SIGNED_IN_DEVICES_MANAGER_H__