Dart: Fix bug in unbind() for Stubs.

Dart: Fix bug in unbind() for Stubs.

The MojoHandleWatcher.remove() in MojoEventSubscription's
unsubscribe() call can race with the removal of a handle
from the handle watcher for an arriving event.

This CL adds a test that recreates this situation, and
removes an assert that fires when it happens.

R=johnmccutchan@google.com

Committed: https://chromium.googlesource.com/external/mojo/+/aaeb3451ba80ead4583ee24773562aee4ef83ef5

[zra, 2016-04-07 21:43:04]

Description was changed from

==========
Dart: Fix bug in unbind() for Stubs.
==========

to

==========
Dart: Fix bug in unbind() for Stubs.

The MojoHandleWatcher.remove() in MojoEventSubscription's
unsubscribe() call can race with the removal of a handle
from the handle watcher for an arriving event.

This CL adds a test that recreates this situation, and
removes an assert that fires when it happens.
==========

[zra, 2016-04-07 21:55:30]

zra@google.com changed reviewers:
+ johnmccutchan@google.com

[Cutch, 2016-04-13 19:59:16]

lgtm

[zra, 2016-04-14 21:34:29]

Description was changed from

==========
Dart: Fix bug in unbind() for Stubs.

The MojoHandleWatcher.remove() in MojoEventSubscription's
unsubscribe() call can race with the removal of a handle
from the handle watcher for an arriving event.

This CL adds a test that recreates this situation, and
removes an assert that fires when it happens.
==========

to

==========
Dart: Fix bug in unbind() for Stubs.

The MojoHandleWatcher.remove() in MojoEventSubscription's
unsubscribe() call can race with the removal of a handle
from the handle watcher for an arriving event.

This CL adds a test that recreates this situation, and
removes an assert that fires when it happens.

R=johnmccutchan@google.com

Committed:
https://chromium.googlesource.com/external/mojo/+/aaeb3451ba80ead4583ee247735...
==========

[zra, 2016-04-14 21:34:31]

Committed patchset #3 (id:40001) manually as
aaeb3451ba80ead4583ee24773562aee4ef83ef5 (presubmit successful).