Use a direct include of strings headers in base/.

base/strings/string_number_conversions.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_STRINGS_STRING_NUMBER_CONVERSIONS_H_
 #define BASE_STRINGS_STRING_NUMBER_CONVERSIONS_H_
 
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/strings/string_piece.h"
 
 // ----------------------------------------------------------------------------
 // IMPORTANT MESSAGE FROM YOUR SPONSOR
 //
 // This file contains no "wstring" variants. New code should use string16. If
 // you need to make old code work, use the UTF8 version and convert. Please do
 // not add wstring variants.
 //
 // Please do not add "convenience" functions for converting strings to integers
@@ skipping 89 matching lines @@
 // Similar to the previous functions, except that output is a vector of bytes.
 // |*output| will contain as many bytes as were successfully parsed prior to the
 // error.  There is no overflow, but input.size() must be evenly divisible by 2.
 // Leading 0x or +/- are not allowed.
 BASE_EXPORT bool HexStringToBytes(const std::string& input,
                                   std::vector<uint8>* output);
 
 }  // namespace base
 
 #endif  // BASE_STRINGS_STRING_NUMBER_CONVERSIONS_H_