Use a direct include of strings headers in url/, win8/.

win8/metro_driver/file_picker_ash.h

 // 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.
 #ifndef CHROME_BROWSER_UI_METRO_DRIVER_FILE_PICKER_ASH_H_
 #define CHROME_BROWSER_UI_METRO_DRIVER_FILE_PICKER_ASH_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 class ChromeAppViewAsh;
 struct MetroViewerHostMsg_SaveAsDialogParams;
 
 namespace base {
 class FilePath;
 }
 
 // Base class for the file pickers.
 class FilePickerSessionBase {
@@ skipping 135 matching lines @@
       FolderPickerAsyncOp;
 
   // Called asynchronously when the folder picker is done.
   HRESULT FolderPickerDone(FolderPickerAsyncOp* async, AsyncStatus status);
 
   DISALLOW_COPY_AND_ASSIGN(FolderPickerSession);
 };
 
 #endif  // CHROME_BROWSER_UI_METRO_DRIVER_FILE_PICKER_ASH_H_