Refactor the devserver to make it easier to control caching

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

 # 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.
 
 import base64
 
 from appengine_wrappers import urlfetch
 from future import Future
 
 class _AsyncFetchDelegate(object):
   def __init__(self, rpc):
     self._rpc = rpc
 
   def Get(self):
     return self._rpc.get_result()
 
 def _MakeHeaders(username, password):
   headers = { 'Cache-Control': 'max-age=0' }
   if username is not None and password is not None:
     headers['Authorization'] = 'Basic %s' % base64.encodestring(
         '%s:%s' % (username, password))
   return headers
 
 class AppEngineUrlFetcher(object):
   """A wrapper around the App Engine urlfetch module that allows for easy
   async fetches.
   """
-  def __init__(self, base_path):
+  def __init__(self, base_path=None):
     self._base_path = base_path
 
   def Fetch(self, url, username=None, password=None):
     """Fetches a file synchronously.
     """
     headers = _MakeHeaders(username, password)
     if self._base_path is not None:
       return urlfetch.fetch('%s/%s' % (self._base_path, url), headers=headers)
     else:
       return urlfetch.fetch(url, headers={ 'Cache-Control': 'max-age=0' })
 
   def FetchAsync(self, url, username=None, password=None):
     """Fetches a file asynchronously, and returns a Future with the result.
     """
     rpc = urlfetch.create_rpc()
     headers = _MakeHeaders(username, password)
     if self._base_path is not None:
       urlfetch.make_fetch_call(rpc,
                                '%s/%s' % (self._base_path, url),
                                headers=headers)
     else:
       urlfetch.make_fetch_call(rpc, url, headers=headers)
     return Future(delegate=_AsyncFetchDelegate(rpc))