Use a direct include of strings headers in base/.

base/win/metro.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.
 
 #ifndef BASE_WIN_METRO_H_
 #define BASE_WIN_METRO_H_
 
 #include <windows.h>
 #include <wpcapi.h>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace base {
 namespace win {
 
 // Identifies the type of the metro launch.
 enum MetroLaunchType {
   METRO_LAUNCH,
   METRO_SEARCH,
   METRO_SHARE,
   METRO_FILE,
@@ skipping 105 matching lines @@
 
 // Function to un-pin a site-specific tile (bookmark) from the start screen.
 typedef void (*MetroUnPinFromStartScreen)(
     const string16& title_id,
     const MetroPinUmaResultCallback& callback);
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_METRO_H_