Add check for null pointer

Add check for null pointer

When resources are freed, asynchronous tasks may fail later and cause
promises to be rejected. However, since the resource is gone, this
crashes. Add a check that the ExecutionContext still exists before
using it.

BUG=644269
TEST=test case doesn't crash

Committed: https://crrev.com/d0abaf6c13603474382963075424bf7586558d74
Cr-Commit-Position: refs/heads/master@{#416797}

[jrummell, 2016-09-06 20:41:28]

jrummell@chromium.org changed reviewers:
+ ddorwin@chromium.org

[jrummell, 2016-09-06 20:41:29]

PTAL

[ddorwin, 2016-09-06 22:09:44]

lgtm

[jrummell, 2016-09-06 22:26:36]

The CQ bit was checked by jrummell@chromium.org

[commit-bot: I haz the power, 2016-09-06 22:27:26]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-07 00:32:42]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-07 00:35:19]

Description was changed from

==========
Add check for null pointer

When resources are freed, asynchronous tasks may fail later and cause
promises to be rejected. However, since the resource is gone, this
crashes. Add a check that the ExecutionContext still exists before
using it.

BUG=644269
TEST=test case doesn't crash
==========

to

==========
Add check for null pointer

When resources are freed, asynchronous tasks may fail later and cause
promises to be rejected. However, since the resource is gone, this
crashes. Add a check that the ExecutionContext still exists before
using it.

BUG=644269
TEST=test case doesn't crash

Committed: https://crrev.com/d0abaf6c13603474382963075424bf7586558d74
Cr-Commit-Position: refs/heads/master@{#416797}
==========

[commit-bot: I haz the power, 2016-09-07 00:35:20]

Patchset 1 (id:??) landed as
https://crrev.com/d0abaf6c13603474382963075424bf7586558d74
Cr-Commit-Position: refs/heads/master@{#416797}