Use a direct include of strings headers in chrome/auto*/.

chrome/browser/autocomplete/zero_suggest_provider.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.
 //
 // This file contains the zero-suggest autocomplete provider. This experimental
 // provider is invoked when the user focuses in the omnibox prior to editing,
 // and generates search query suggestions based on the current URL. To enable
 // this provider, point --experimental-zero-suggest-url-prefix at an
 // appropriate suggestion service.
 //
 // HUGE DISCLAIMER: This is just here for experimenting and will probably be
 // deleted entirely as we revise how suggestions work with the omnibox.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_ZERO_SUGGEST_PROVIDER_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_ZERO_SUGGEST_PROVIDER_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "chrome/browser/autocomplete/autocomplete_provider.h"
 #include "chrome/browser/autocomplete/search_provider.h"
 #include "net/url_request/url_fetcher_delegate.h"
 
 class AutocompleteInput;
 class GURL;
 class TemplateURLService;
 
 namespace base {
 class ListValue;
@@ skipping 140 matching lines @@
   // Whether a zero suggest request triggered a field trial in the omnibox
   // session.  The user could have clicked on a suggestion when zero suggest
   // triggered (same condition as field_trial_triggered_), or triggered zero
   // suggest but kept typing.
   bool field_trial_triggered_in_session_;
 
   DISALLOW_COPY_AND_ASSIGN(ZeroSuggestProvider);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_ZERO_SUGGEST_PROVIDER_H_