[md_browser] Add markdown.extensions.def_list to list of supported extensions.

tools/md_browser/md_browser.py

 # Copyright 2015 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.
 
 """Simple Markdown browser for a Git checkout."""
 from __future__ import print_function
 
 import SimpleHTTPServer
 import SocketServer
 import argparse
@@ skipping 83 matching lines @@
       self._WriteTemplate('doc.css')
     elif not os.path.exists(full_path):
       self._DoNotFound()
     elif path.lower().endswith('.md'):
       self._DoMD(path)
     else:
       self._DoUnknown()
 
   def _DoMD(self, path):
     extensions = [
+        'markdown.extensions.def_list',
         'markdown.extensions.fenced_code',
         'markdown.extensions.tables',
         'markdown.extensions.toc',
         'gitiles_ext_blocks',
     ]
     extension_configs = {
         'markdown.extensions.toc': {
             'slugify': _gitiles_slugify
         },
     }
@@ skipping 23 matching lines @@
     with codecs.open(path, encoding='utf-8') as fp:
       return fp.read()
 
   def _WriteTemplate(self, template):
     contents = self._Read(os.path.join('tools', 'md_browser', template))
     self.wfile.write(contents.encode('utf-8'))
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))