components: Cleanup class/struct fwd declarations

components/omnibox/browser/in_memory_url_index.h

 // Copyright (c) 2012 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 COMPONENTS_OMNIBOX_BROWSER_IN_MEMORY_URL_INDEX_H_
 #define COMPONENTS_OMNIBOX_BROWSER_IN_MEMORY_URL_INDEX_H_
 
 #include <stddef.h>
 
 #include <functional>
@@ skipping 22 matching lines @@
 
 namespace base {
 class SequencedTaskRunner;
 class Time;
 }
 
 namespace bookmarks {
 class BookmarkModel;
 }
 
-namespace in_memory_url_index {
-class InMemoryURLIndexCacheItem;
-}
-
 namespace history {
 class HistoryDatabase;
 class HistoryService;
 class HQPPerfTestOnePopularURL;
 }
 
 class URLIndexPrivateData;
 
 typedef std::set<std::string> SchemeSet;
 
@@ skipping 260 matching lines @@
   // This flag is set to true if we want to listen to the
   // HistoryServiceLoaded Notification.
   bool listen_to_history_service_loaded_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(InMemoryURLIndex);
 };
 
 #endif  // COMPONENTS_OMNIBOX_BROWSER_IN_MEMORY_URL_INDEX_H_