Docs: Use ETags.

chrome/common/extensions/docs/server2/local_renderer.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 render_servlet import RenderServlet
 from server_instance import ServerInstance
 from servlet import Request
 
 class _LocalRenderServletDelegate(object):
   def CreateServerInstance(self):
     return ServerInstance.ForLocal()
 
 class LocalRenderer(object):
   '''Renders pages fetched from the local file system.
   '''
   @staticmethod
-  def Render(path):
+  def Render(path, headers=None):
     assert not '\\' in path
-    return RenderServlet(Request.ForTest(path),
+    return RenderServlet(Request.ForTest(path, headers=headers),
                          _LocalRenderServletDelegate()).Get()