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

printing/backend/print_backend_win.cc

 // Copyright (c) 2012 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 "printing/backend/print_backend.h"
 
 #include <objidl.h>
 #include <winspool.h>
 
 #include "base/memory/scoped_ptr.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/utf_string_conversions.h"
 #include "base/win/scoped_bstr.h"
 #include "base/win/scoped_comptr.h"
 #include "base/win/scoped_hglobal.h"
 #include "printing/backend/print_backend_consts.h"
 #include "printing/backend/printing_info_win.h"
 #include "printing/backend/win_helper.h"
 
 
 namespace {
@@ skipping 233 matching lines @@
               printer_handle.Receive(), NULL);
   return printer_handle.IsValid();
 }
 
 scoped_refptr<PrintBackend> PrintBackend::CreateInstance(
     const base::DictionaryValue* print_backend_settings) {
   return new PrintBackendWin;
 }
 
 }  // namespace printing