Use a direct include of strings headers in chrome/browser/r*-s*/.

chrome/browser/signin/oauth2_token_service_test_util.h

 // Copyright 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.
 
 #ifndef CHROME_BROWSER_SIGNIN_OAUTH2_TOKEN_SERVICE_TEST_UTIL_H_
 #define CHROME_BROWSER_SIGNIN_OAUTH2_TOKEN_SERVICE_TEST_UTIL_H_
 
 #include "chrome/browser/signin/oauth2_token_service.h"
 
 #include <string>
 
-#include "base/stringprintf.h"
+#include "base/strings/stringprintf.h"
 #include "google_apis/gaia/google_service_auth_error.h"
 
 extern const char kValidTokenResponse[];
 
 std::string GetValidTokenResponse(std::string token, int expiration);
 
 // A simple testing consumer.
 class TestingOAuth2TokenServiceConsumer : public OAuth2TokenService::Consumer {
  public:
   TestingOAuth2TokenServiceConsumer();
   virtual ~TestingOAuth2TokenServiceConsumer();
 
   // OAuth2TokenService::Consumer overrides.
   virtual void OnGetTokenSuccess(const OAuth2TokenService::Request* request,
                                  const std::string& token,
                                  const base::Time& expiration_date) OVERRIDE;
   virtual void OnGetTokenFailure(const OAuth2TokenService::Request* request,
                                  const GoogleServiceAuthError& error) OVERRIDE;
 
   std::string last_token_;
   int number_of_successful_tokens_;
   GoogleServiceAuthError last_error_;
   int number_of_errors_;
 };
 
 #endif  // CHROME_BROWSER_SIGNIN_OAUTH2_TOKEN_SERVICE_TEST_UTIL_H_