Avoid closing an already closed channel

Avoid closing an already closed channel

R=devoncarew@google.com

Committed: https://github.com/dart-lang/sdk/commit/6f96d88e1e19c194edd2142f89703cb7484871df

[Brian Wilkerson, 2017-08-17 15:50:21]

brianwilkerson@google.com changed reviewers:
+ devoncarew@google.com, scheglov@google.com

[Brian Wilkerson, 2017-08-17 15:50:22]

This is based on an internally reported exception.

It appears that the method `handleOnDone` can be called after the channel has
been set to `null`. The most likely scenario seems to be that it's set to `null`
on line 1012 when we're closing the connection, and that between the expiration
of the timeout and the execution of the `then` closure we're getting
notification from the plugin's isolate that it has completed. I don't know
whether that's a possible scenario, though.

In any case, I don't think it will cause any harm to test for `null` before
invoking `close`.

[devoncarew, 2017-08-17 16:33:36]

lgtm

[Brian Wilkerson, 2017-08-17 16:47:37]

Description was changed from

==========
Avoid closing an already closed channel
==========

to

==========
Avoid closing an already closed channel

R=devoncarew@google.com

Committed:
https://github.com/dart-lang/sdk/commit/6f96d88e1e19c194edd2142f89703cb7484871df
==========

[Brian Wilkerson, 2017-08-17 16:47:39]

Committed patchset #1 (id:1) manually as
6f96d88e1e19c194edd2142f89703cb7484871df (presubmit successful).