Extension docs: Include sidenav in 404 pages

chrome/common/extensions/docs/server2/render_servlet.py

 # Copyright 2013 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.
 
 from fnmatch import fnmatch
 import logging
 import mimetypes
 import os
 import traceback
 
@@ skipping 72 matching lines @@
         content_type = mimetype
       elif path.endswith('.html'):
         content = templates.Render(path)
         content_type = 'text/html'
     except FileNotFoundError as e:
       logging.warning(traceback.format_exc())
       content = None
 
     headers = {'x-frame-options': 'sameorigin'}
     if content is None:
-      return Response.NotFound(templates.Render('404'), headers=headers)
+      doc_class = path.split('/', 1)[0]
+      content = templates.Render('%s/404' % doc_class)
+      if not content:
+        content = templates.Render('extensions/404')
+      return Response.NotFound(content, headers=headers)
 
     if not content:
       logging.error('%s had empty content' % path)
 
     headers.update({
       'content-type': content_type,
       'cache-control': 'max-age=300',
     })
     return Response.Ok(content, headers=headers)