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

chrome/browser/chromeos/policy/user_cloud_policy_store_chromeos.cc

 // 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.
 
 #include "chrome/browser/chromeos/policy/user_cloud_policy_store_chromeos.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
-#include "base/stringprintf.h"
+#include "base/strings/stringprintf.h"
 #include "chrome/browser/chromeos/policy/user_policy_disk_cache.h"
 #include "chrome/browser/chromeos/policy/user_policy_token_loader.h"
 #include "chrome/browser/policy/proto/cloud/device_management_local.pb.h"
 #include "chromeos/dbus/cryptohome_client.h"
 #include "chromeos/dbus/session_manager_client.h"
 #include "content/public/browser/browser_thread.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 #include "policy/proto/cloud_policy.pb.h"
 
 namespace em = enterprise_management;
@@ skipping 462 matching lines @@
       !sanitized_username.empty()) {
     policy_key_path_ = user_policy_key_dir_.Append(
         base::StringPrintf(kPolicyKeyFile, sanitized_username.c_str()));
   } else {
     SampleValidationFailure(VALIDATION_FAILURE_DBUS);
   }
   ReloadPolicyKey(callback);
 }
 
 }  // namespace policy