Add async_helper package.

Add async_helper package.

This package is private and should not be published to pub (nor should
its documentation be published to api.dartlang.org).

R=kustermann@google.com

Committed: https://code.google.com/p/dart/source/detail?r=26774

[floitsch, 2013-08-27 13:03:39]

I haven't tested the publish-package script, so please be extra-vigilant on that
one.

[kustermann, 2013-08-27 14:29:30]

LGTM

But we should not maintain two versions. Why not converting the current tests to
use this package as well?

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml
File pkg/async_helper/pubspec.yaml (right):

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml...
pkg/async_helper/pubspec.yaml:4: description: >
Remove the ">"?

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml...
pkg/async_helper/pubspec.yaml:6: make use of the Dart unit test library - for
example, the core
"unit test" -> "unittest".

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml...
pkg/async_helper/pubspec.yaml:9: the facilities provided in the unit test
library.
ditto.

[floitsch, 2013-08-28 09:22:46]

I will convert the tests in a separate CL.
I prefer to keep CLs smaller.

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml
File pkg/async_helper/pubspec.yaml (right):

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml...
pkg/async_helper/pubspec.yaml:4: description: >
On 2013/08/27 14:29:30, kustermann wrote:
> Remove the ">"?

This is yaml syntax stating that new-lines should be folded.

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml...
pkg/async_helper/pubspec.yaml:6: make use of the Dart unit test library - for
example, the core
On 2013/08/27 14:29:30, kustermann wrote:
> "unit test" -> "unittest".

Done.

https://codereview.chromium.org/23547005/diff/1/pkg/async_helper/pubspec.yaml...
pkg/async_helper/pubspec.yaml:9: the facilities provided in the unit test
library.
On 2013/08/27 14:29:30, kustermann wrote:
> ditto.

Done.

[floitsch, 2013-08-28 09:25:00]

Committed patchset #2 manually as r26774 (presubmit successful).