Add StreamSubscription.asFuture.

Add StreamSubscription.asFuture.

Committed: https://code.google.com/p/dart/source/detail?r=21441

[blois, 2013-04-13 00:38:27]

DOM changes lgtm.

[Anders Johnsen, 2013-04-15 09:15:47]

lgtm

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:965: cancel();
Set unsubscribeOnError = true?

[Lasse Reichstein Nielsen, 2013-04-15 10:19:15]

lgtm

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream.dart
File sdk/lib/async/stream.dart (right):

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream.dart#new...
sdk/lib/async/stream.dart:843: * when it was listening with `unsubscribeOnError`
set to `false`).
"This also makes the subscription cancel on any error".

(Rename unsubscribeOnError to cancelOnError everywhere?)

What happens if you use asFuture, and then set a new onError handler,
overwriting the Future's handler? Will it still cancel on error or not?

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:965: cancel();
It's final, and if you overwrite onError again, which you still can, it won't
change back.

[floitsch, 2013-04-15 12:16:37]

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream.dart
File sdk/lib/async/stream.dart (right):

https://codereview.chromium.org/14237002/diff/1/sdk/lib/async/stream.dart#new...
sdk/lib/async/stream.dart:843: * when it was listening with `unsubscribeOnError`
set to `false`).
On 2013/04/15 10:19:15, Lasse Reichstein Nielsen wrote:
> "This also makes the subscription cancel on any error".
> 
> (Rename unsubscribeOnError to cancelOnError everywhere?)
> 
> What happens if you use asFuture, and then set a new onError handler,
> overwriting the Future's handler? Will it still cancel on error or not?

If you change the onError handler it won't receive the error and thus not
cancel.
I'm almost tempted to make the listener functions on Subscription private...

[floitsch, 2013-04-15 12:17:22]

Committed patchset #1 manually as r21441 (presubmit successful).