Add FutureGroup.onIdle and FutureGroup.isIdle.

Add FutureGroup.onIdle and FutureGroup.isIdle.

R=lrn@google.com

Committed: https://github.com/dart-lang/async/commit/f17906cd2a0dee8956a312b30bd04ef9b12c161f

[nweiz, 2015-07-01 20:52:28]

nweiz@google.com changed reviewers:
+ lrn@google.com

[Lasse Reichstein Nielsen, 2015-07-02 09:18:36]

lgtm

https://codereview.chromium.org/1215063008/diff/1/lib/src/future_group.dart
File lib/src/future_group.dart (right):

https://codereview.chromium.org/1215063008/diff/1/lib/src/future_group.dart#n...
lib/src/future_group.dart:47: final _onIdleController = new
StreamController.broadcast(sync: true);
Could it be worth it to only create this controller the first time onIdle is
read? It means some "if (_onIdleController != null)" guards below, but it avoids
creating a controller if it isn't used.

[nweiz, 2015-07-06 20:23:15]

Code review changes

[nweiz, 2015-07-06 20:23:18]

https://codereview.chromium.org/1215063008/diff/1/lib/src/future_group.dart
File lib/src/future_group.dart (right):

https://codereview.chromium.org/1215063008/diff/1/lib/src/future_group.dart#n...
lib/src/future_group.dart:47: final _onIdleController = new
StreamController.broadcast(sync: true);
On 2015/07/02 09:18:35, Lasse Reichstein Nielsen wrote:
> Could it be worth it to only create this controller the first time onIdle is
> read? It means some "if (_onIdleController != null)" guards below, but it
avoids
> creating a controller if it isn't used.

Done.

[nweiz, 2015-07-06 20:24:39]

Committed patchset #2 (id:20001) manually as
f17906cd2a0dee8956a312b30bd04ef9b12c161f (presubmit successful).