components: Cleanup class/struct fwd declarations

components/web_cache/browser/web_cache_manager.h

 // Copyright (c) 2011 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.
 
 // This is the browser side of the cache manager, it tracks the activity of the
 // render processes and allocates available memory cache resources.
 
 #ifndef COMPONENTS_WEB_CACHE_BROWSER_WEB_CACHE_MANAGER_H_
 #define COMPONENTS_WEB_CACHE_BROWSER_WEB_CACHE_MANAGER_H_
 
@@ skipping 10 matching lines @@
 #include "base/time/time.h"
 #include "components/web_cache/public/interfaces/web_cache.mojom.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 namespace base {
 template<typename Type>
 struct DefaultSingletonTraits;
 }  // namespace base
 
-class PrefRegistrySimple;
-
 namespace web_cache {
 
 // Note: memory usage uses uint64_t because potentially the browser could be
 // 32 bit and the renderers 64 bits.
 class WebCacheManager : public content::NotificationObserver {
   friend class WebCacheManagerTest;
   FRIEND_TEST_ALL_PREFIXES(
       WebCacheManagerTest,
       GatherStatsTest);
   FRIEND_TEST_ALL_PREFIXES(
@@ skipping 223 matching lines @@
   WebCacheServicesMap web_cache_services_;
 
   base::WeakPtrFactory<WebCacheManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WebCacheManager);
 };
 
 }  // namespace web_cache
 
 #endif  // COMPONENTS_WEB_CACHE_BROWSER_WEB_CACHE_MANAGER_H_