Move string files in base/ to the string subdirectory.

base/strings/string_util.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 working with strings.
 
-#ifndef BASE_STRING_UTIL_H_
-#define BASE_STRING_UTIL_H_
+#ifndef BASE_STRINGS_STRING_UTIL_H_
+#define BASE_STRINGS_STRING_UTIL_H_
 
 #include <ctype.h>
 #include <stdarg.h>   // va_list
 
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 547 matching lines @@
   typedef unsigned short Unsigned;
 #elif defined(WCHAR_T_IS_UTF32)
   typedef uint32 Unsigned;
 #endif
 };
 template<>
 struct ToUnsigned<short> {
   typedef unsigned short Unsigned;
 };
 
-#endif  // BASE_STRING_UTIL_H_
+#endif  // BASE_STRINGS_STRING_UTIL_H_