base: Update the include paths of base/string_piece.h to its new location.

base/strings/string_tokenizer.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.
 
 #ifndef BASE_STRINGS_STRING_TOKENIZER_H_
 #define BASE_STRINGS_STRING_TOKENIZER_H_
 
 #include <algorithm>
 #include <string>
 
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 
 namespace base {
 
 // StringTokenizerT is a simple string tokenizer class.  It works like an
 // iterator that with each step (see the Advance method) updates members that
 // refer to the next token in the input string.  The user may optionally
 // configure the tokenizer to return delimiters.
 //
 // Warning: be careful not to pass a C string into the 2-arg constructor:
 // StringTokenizer t("this is a test", " ");  // WRONG
@@ skipping 229 matching lines @@
 
 typedef StringTokenizerT<std::string, std::string::const_iterator>
     StringTokenizer;
 typedef StringTokenizerT<std::wstring, std::wstring::const_iterator>
     WStringTokenizer;
 typedef StringTokenizerT<std::string, const char*> CStringTokenizer;
 
 }  // namespace base
 
 #endif  // BASE_STRINGS_STRING_TOKENIZER_H_