def _double_prefix(deque):
    new_len = max(len(deque[0]) * 2,
                  (len(deque[0]) + len(deque[1])))
    _merge_prefix(deque, new_len)
Grow by doubling, but don't split the second chunk just because the
dataset/ETHPy150Open RobotWebTools/rosbridge_suite/rosbridge_server/src/tornado/iostream.py/_double_prefix