Cleanup: Remove unneeded forward declarations from various chrome/browser subdirectories.

chrome/browser/autocomplete/history_quick_provider.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.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_HISTORY_QUICK_PROVIDER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_HISTORY_QUICK_PROVIDER_H_
 #pragma once
 
 #include <string>
 
 #include "chrome/browser/autocomplete/autocomplete_match.h"
 #include "chrome/browser/autocomplete/history_provider.h"
 #include "chrome/browser/history/history_types.h"
 #include "chrome/browser/history/in_memory_url_index.h"
 
 class Profile;
 class TermMatches;
 
-namespace history {
-class HistoryBackend;
-}  // namespace history
-
 // This class is an autocomplete provider (a pseudo-internal component of
 // the history system) which quickly (and synchronously) provides matching
 // results from recently or frequently visited sites in the profile's
 // history.
 class HistoryQuickProvider : public HistoryProvider {
  public:
   HistoryQuickProvider(ACProviderListener* listener, Profile* profile);
 
   virtual ~HistoryQuickProvider();
 
@@ skipping 56 matching lines @@
   std::string languages_;
 
   // Only used for testing.
   scoped_ptr<history::InMemoryURLIndex> index_for_testing_;
 
   // This provider is disabled when true.
   static bool disabled_;
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_HISTORY_QUICK_PROVIDER_H_