'Builds a single Push Promise frame.'

def buildPushPromiseFrame(self, streamID, promisedStreamID, headers, flags=[]):

    f = hyperframe.frame.PushPromiseFrame(streamID)
    f.promised_stream_id = promisedStreamID
    f.data = self.encoder.encode(headers)
    f.flags = set(flags)
    f.flags.add('END_HEADERS')
    return f
