Use JS Date().toLocaleDateString() to format date in header.

chrome/renderer/mock_printer.h

 // 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.
 
 #ifndef CHROME_RENDERER_MOCK_PRINTER_H_
 #define CHROME_RENDERER_MOCK_PRINTER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 134 matching lines @@
   bool is_first_request_;
   bool print_to_pdf_;
   int preview_request_id_;
 
   // Specifies whether to retain/crop/scale source page size to fit the
   // given printable area.
   WebKit::WebPrintScalingOption print_scaling_option_;
 
   // Used for displaying headers and footers.
   bool display_header_footer_;
-  string16 date_;
   string16 title_;
   string16 url_;
 
   // Used for generating invalid settings.
   bool use_invalid_settings_;
 
   std::vector<scoped_refptr<MockPrinterPage> > pages_;
 
   DISALLOW_COPY_AND_ASSIGN(MockPrinter);
 };
 
 #endif  // CHROME_RENDERER_MOCK_PRINTER_H_