My machine is behind proxy. httplib2 fails to connect accounts.google.com.

What steps will reproduce the problem?
> depot-tools-auth login https://codereview.chromium.org --verbose
Your browser has been opened to visit:

    https://accounts.google.com/o/oauth2/auth?XXXXXXXXXXXXXX

Created new window in existing browser session.
Traceback (most recent call last):
  File "/home/dshwang/chromium/depot_tools/depot-tools-auth.py", line 99, in <module>
    sys.exit(main(sys.argv[1:]))
  File "/home/dshwang/chromium/depot_tools/depot-tools-auth.py", line 90, in main
    return dispatcher.execute(OptionParser(), argv)
  File "/home/dshwang/chromium/depot_tools/subcommand.py", line 252, in execute
    return command(parser, args[1:])
  File "/home/dshwang/chromium/depot_tools/depot-tools-auth.py", line 32, in CMDlogin
    authenticator.login()
  File "/home/dshwang/chromium/depot_tools/auth.py", line 270, in login
    force_refresh=True, allow_user_interaction=True)
  File "/home/dshwang/chromium/depot_tools/auth.py", line 321, in get_access_token
    self._access_token = self._create_access_token(allow_user_interaction)
  File "/home/dshwang/chromium/depot_tools/auth.py", line 500, in _create_access_token
    credentials = _run_oauth_dance(self._config, self._scopes)
  File "/home/dshwang/chromium/depot_tools/auth.py", line 646, in _run_oauth_dance
    return flow.step2_exchange(code)
  File "/home/dshwang/chromium/depot_tools/third_party/oauth2client/util.py", line 132, in positional_wrapper
    return wrapped(*args, **kwargs)
  File "/home/dshwang/chromium/depot_tools/third_party/oauth2client/client.py", line 1282, in step2_exchange
    headers=headers)
  File "/home/dshwang/chromium/depot_tools/third_party/httplib2/__init__.py", line 1593, in request
    (response, content) = self._request(conn, authority, uri, request_uri, method, body, headers, redirections, cachekey)
  File "/home/dshwang/chromium/depot_tools/third_party/httplib2/__init__.py", line 1335, in _request
    (response, content) = self._conn_request(conn, request_uri, method, body, headers)
  File "/home/dshwang/chromium/depot_tools/third_party/httplib2/__init__.py", line 1263, in _conn_request
    raise ServerNotFoundError("Unable to find the server at %s" % conn.host)
third_party.httplib2.ServerNotFoundError: Unable to find the server at accounts.google.com