Use a direct include of strings headers in base/.

base/win/win_util.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.
 
 // =============================================================================
 // PLEASE READ
 //
 // In general, you should not be adding stuff to this file.
 //
 // - If your thing is only used in one place, just put it in a reasonable
 //   location in or near that one place. It's nice you want people to be able
 //   to re-use your function, but realistically, if it hasn't been necessary
 //   before after so many years of development, it's probably not going to be
 //   used in other places in the future unless you know of them now.
 //
 // - If your thing is used by multiple callers and is UI-related, it should
 //   probably be in app/win/ instead. Try to put it in the most specific file
 //   possible (avoiding the *_util files when practical).
 //
 // =============================================================================
 
 #ifndef BASE_WIN_WIN_UTIL_H_
 #define BASE_WIN_WIN_UTIL_H_
 
 #include <windows.h>
 
 #include <string>
 
 #include "base/base_export.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 struct IPropertyStore;
 struct _tagpropertykey;
 typedef _tagpropertykey PROPERTYKEY;
 
 namespace base {
 namespace win {
 
 BASE_EXPORT void GetNonClientMetrics(NONCLIENTMETRICS* metrics);
 
@@ skipping 77 matching lines @@
 BASE_EXPORT bool DisplayVirtualKeyboard();
 
 // Dismisses the on screen keyboard if it is being displayed on Windows 8 and.
 // above. Returns true on success.
 BASE_EXPORT bool DismissVirtualKeyboard();
 
 }  // namespace win
 }  // namespace base
 
 #endif  // BASE_WIN_WIN_UTIL_H_