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

chrome/browser/autocomplete/history_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_PROVIDER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_HISTORY_PROVIDER_H_
 #pragma once
 
 #include "base/compiler_specific.h"
 #include "chrome/browser/autocomplete/autocomplete.h"
 
-namespace history {
-
-class HistoryBackend;
-class URLDatabase;
-class URLRow;
-
-}  // namespace history
-
 // This class is a base class for the history autocomplete providers and
 // provides functions useful to all derived classes.
 class HistoryProvider : public AutocompleteProvider {
  public:
   virtual void DeleteMatch(const AutocompleteMatch& match) OVERRIDE;
 
  protected:
   HistoryProvider(ACProviderListener* listener,
                   Profile* profile,
                   const char* name);
@@ skipping 20 matching lines @@
 
   // Returns true if inline autocompletion should be prevented. Use this instead
   // of |input.prevent_inline_autocomplete| if the input is passed through
   // FixupUserInput(). This method returns true if
   // |input.prevent_inline_autocomplete()| is true, or the input text contains
   // trailing whitespace.
   bool PreventInlineAutocomplete(const AutocompleteInput& input);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_HISTORY_PROVIDER_H_