Convert StreamWriter.drain() to a classic coroutine

Convert StreamWriter.drain() to a classic coroutine

[GvR, 2014-07-21 22:36:12]

I think the basic idea is sound, I am just not 100% sure about the right class
structure, since this is a Mixin class.

https://codereview.appspot.com/116970044/diff/20001/asyncio/streams.py
File asyncio/streams.py (right):

https://codereview.appspot.com/116970044/diff/20001/asyncio/streams.py#newcod...
asyncio/streams.py:144: StreamWriter.drain() must wait for _make_drain_waiter()
coroutine.
I propose to rename _make_drain_waiter() to _drain_helper(), just so that code
that was calling or overriding it will break in an obvious way. (The original
text of the docstring suggests that this is a "_protected" method.)

Or maybe we should just make the helper a public method introduced by this mixin
class? I don't like the "_protected" convention much...

https://codereview.appspot.com/116970044/diff/20001/asyncio/streams.py#newcod...
asyncio/streams.py:295: This method is a coroutine.
You don't have to say that, the decorator already says it.

[haypo_gmail, 2014-07-21 22:46:48]

New version addressing last comments.

[GvR, 2014-07-21 23:23:27]

LGTM.

(On second thought this is good enough.)