Use a direct include of strings headers in base/.

base/strings/string_util.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.
 //
 // This file defines utility functions for working with strings.
 
 #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"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/strings/string_piece.h"  // For implicit conversions.
 
 // Safe standard library wrappers for all platforms.
 
 namespace base {
 
 // C standard-library functions like "strncasecmp" and "snprintf" that aren't
 // cross-platform are provided as "base::strncasecmp", and their prototypes
 // are listed below.  These functions are then implemented as inline calls
 // to the platform-specific equivalents in the platform-specific headers.
@@ skipping 109 matching lines @@
 template<typename Char> struct CaseInsensitiveCompareASCII {
  public:
   bool operator()(Char x, Char y) const {
     return ToLowerASCII(x) == ToLowerASCII(y);
   }
 };
 
 }  // namespace base
 
 #if defined(OS_WIN)
-#include "base/string_util_win.h"
+#include "base/strings/string_util_win.h"
 #elif defined(OS_POSIX)
-#include "base/string_util_posix.h"
+#include "base/strings/string_util_posix.h"
 #else
 #error Define string operations appropriately for your platform
 #endif
 
 // These threadsafe functions return references to globally unique empty
 // strings.
 //
 // DO NOT USE THESE AS A GENERAL-PURPOSE SUBSTITUTE FOR DEFAULT CONSTRUCTORS.
 // There is only one case where you should use these: functions which need to
 // return a string by reference (e.g. as a class member accessor), and don't
@@ skipping 405 matching lines @@
 #elif defined(WCHAR_T_IS_UTF32)
   typedef uint32 Unsigned;
 #endif
 };
 template<>
 struct ToUnsigned<short> {
   typedef unsigned short Unsigned;
 };
 
 #endif  // BASE_STRINGS_STRING_UTIL_H_