Use a direct include of strings headers in base/.

base/json/string_escape.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.
 //
 // This file defines utility functions for escaping strings.
 
 #ifndef BASE_JSON_STRING_ESCAPE_H_
 #define BASE_JSON_STRING_ESCAPE_H_
 
 #include <string>
 
 #include "base/base_export.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace base {
 
 // Escape |str| appropriately for a JSON string literal, _appending_ the
 // result to |dst|. This will create unicode escape sequences (\uXXXX).
 // If |put_in_quotes| is true, the result will be surrounded in double quotes.
 // The outputted literal, when interpreted by the browser, should result in a
 // javascript string that is identical and the same length as the input |str|.
 BASE_EXPORT void JsonDoubleQuote(const std::string& str,
                                  bool put_in_quotes,
                                  std::string* dst);
 
 // Same as above, but always returns the result double quoted.
 BASE_EXPORT std::string GetDoubleQuotedJson(const std::string& str);
 
 BASE_EXPORT void JsonDoubleQuote(const string16& str,
                                  bool put_in_quotes,
                                  std::string* dst);
 
 // Same as above, but always returns the result double quoted.
 BASE_EXPORT std::string GetDoubleQuotedJson(const string16& str);
 
 }  // namespace base
 
 #endif  // BASE_JSON_STRING_ESCAPE_H_