Use base namespace for string16 in components and cloud_print.

cloud_print/virtual_driver/win/virtual_driver_helpers.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 CLOUD_PRINT_VIRTUAL_DRIVER_WIN_VIRTUAL_DRIVER_HELPERS_H_
 #define CLOUD_PRINT_VIRTUAL_DRIVER_WIN_VIRTUAL_DRIVER_HELPERS_H_
 
 #include <windows.h>
 
 #include "base/strings/string16.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace cloud_print {
 
 // Returns TRUE if the current OS is 64 bit.
 bool IsSystem64Bit();
 
 // Convert an HRESULT to a localized string and display it in a message box.
-void DisplayWindowsMessage(HWND hwnd, HRESULT hr, const string16 &caption);
+void DisplayWindowsMessage(HWND hwnd, HRESULT hr,
+                           const base::string16 &caption);
 
 // Returns the correct port monitor DLL file name for the current machine.
-string16 GetPortMonitorDllName();
+base::string16 GetPortMonitorDllName();
 
 // Gets the standard install path for "version 3" print drivers.
 HRESULT GetPrinterDriverDir(base::FilePath* path);
 
 }  // namespace cloud_print
 
 #endif  // CLOUD_PRINT_VIRTUAL_DRIVER_WIN_VIRTUAL_DRIVER_HELPERS_H_