Use a direct include of strings headers in chrome/browser/chromeos/.

chrome/browser/chromeos/policy/policy_oauth2_token_fetcher.cc

 // Copyright (c) 2013 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.
 
 #include "chrome/browser/chromeos/policy/policy_oauth2_token_fetcher.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/logging.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "content/public/browser/browser_thread.h"
 #include "google_apis/gaia/gaia_auth_fetcher.h"
 #include "google_apis/gaia/gaia_constants.h"
 #include "google_apis/gaia/gaia_urls.h"
 #include "google_apis/gaia/google_service_auth_error.h"
 #include "google_apis/gaia/oauth2_access_token_fetcher.h"
 #include "net/url_request/url_request_context_getter.h"
 
 using content::BrowserThread;
 
@@ skipping 113 matching lines @@
   // So don't rely on |this| still being valid after ForwardPolicyToken()
   // returns i.e. don't write to |failed_| or other fields.
   ForwardPolicyToken(EmptyString());
 }
 
 void PolicyOAuth2TokenFetcher::ForwardPolicyToken(const std::string& token) {
   callback_.Run(token);
 }
 
 }  // namespace policy