Use a direct include of strings headers in base/.

base/strings/latin1_string_conversions.h

 // Copyright 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 BASE_STRINGS_LATIN1_STRING_CONVERSIONS_H_
 #define BASE_STRINGS_LATIN1_STRING_CONVERSIONS_H_
 
 #include <string>
 
 #include "base/base_export.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace base {
 
 // This definition of Latin1Char matches the definition of LChar in Blink. We
 // use unsigned char rather than char to make less tempting to mix and match
 // Latin-1 and UTF-8 characters..
 typedef unsigned char Latin1Char;
 
 // This somewhat odd function is designed to help us convert from Blink Strings
 // to string16. A Blink string is either backed by an array of Latin-1
 // characters or an array of UTF-16 characters. This function is called by
 // WebString::operator string16() to convert one or the other character array
 // to string16. This function is defined here rather than in WebString.h to
 // avoid binary bloat in all the callers of the conversion operator.
 BASE_EXPORT string16 Latin1OrUTF16ToUTF16(size_t length,
                                           const Latin1Char* latin1,
                                           const char16* utf16);
 
 }  // namespace base
 
 #endif  // BASE_STRINGS_LATIN1_STRING_CONVERSIONS_H_