Use a direct include of strings headers in base/.

base/strings/utf_string_conversions.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 BASE_STRINGS_UTF_STRING_CONVERSIONS_H_
 #define BASE_STRINGS_UTF_STRING_CONVERSIONS_H_
 
 #include <string>
 
 #include "base/base_export.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/strings/string_piece.h"
 
 namespace base {
 
 // These convert between UTF-8, -16, and -32 strings. They are potentially slow,
 // so avoid unnecessary conversions. The low-level versions return a boolean
 // indicating whether the conversion was 100% valid. In this case, it will still
 // do the best it can and put the result in the output buffer. The versions that
 // return strings ignore this error and just return the best conversion
 // possible.
@@ skipping 41 matching lines @@
 using base::WideToUTF8;
 using base::UTF8ToWide;
 using base::WideToUTF16;
 using base::UTF16ToWide;
 using base::UTF8ToUTF16;
 using base::UTF16ToUTF8;
 using base::ASCIIToWide;
 using base::ASCIIToUTF16;
 
 #endif  // BASE_STRINGS_UTF_STRING_CONVERSIONS_H_