Use a direct include of strings headers in base/.

base/strings/utf_string_conversions.cc

 // Copyright (c) 2010 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.
 
 #include "base/strings/utf_string_conversions.h"
 
-#include "base/string_util.h"
 #include "base/strings/string_piece.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversion_utils.h"
 
 namespace base {
 
 namespace {
 
 // Generalized Unicode converter -----------------------------------------------
 
 // Converts the given source Unicode character type to the given destination
 // Unicode character type as a STL string. The given input buffer and size
@@ skipping 157 matching lines @@
   DCHECK(IsStringASCII(ascii)) << ascii;
   return std::wstring(ascii.begin(), ascii.end());
 }
 
 string16 ASCIIToUTF16(const StringPiece& ascii) {
   DCHECK(IsStringASCII(ascii)) << ascii;
   return string16(ascii.begin(), ascii.end());
 }
 
 }  // namespace base