Fix TaskmanagerIoThreadHelper bug.

Fix TaskmanagerIoThreadHelper bug.

Deleting the TaskManagerIoThreadHelper should cancel any pending
OnMultipleBytesReadIO calls. If it doesn't, we can sometimes fail the
DCHECK(!bytes_read_buffer_.empty()); check.

BUG=None
TEST=TaskManagerOOPIFBrowserTest.LeavePageWithCrossSiteIframes/0

Committed: https://crrev.com/39b8a004d4f83d3559628b51613891d2f4773304
Cr-Commit-Position: refs/heads/master@{#389889}

[ncarter (slow), 2016-04-26 19:48:58]

The CQ bit was checked by nick@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-04-26 19:49:26]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1918423002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1918423002/1

[ncarter (slow), 2016-04-26 19:51:18]

nick@chromium.org changed reviewers:
+ afakhry@chromium.org

[ncarter (slow), 2016-04-26 19:51:18]

This was uncovered by the old TaskManagerBrowserTests. Please review.

[afakhry, 2016-04-26 20:20:29]

On 2016/04/26 19:51:18, ncarter wrote:
> This was uncovered by the old TaskManagerBrowserTests. Please review.

lgtm ... Thanks for this fix.

[commit-bot: I haz the power, 2016-04-26 21:00:34]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-04-26 21:00:37]

Dry run: This issue passed the CQ dry run.

[ncarter (slow), 2016-04-26 21:10:52]

The CQ bit was checked by nick@chromium.org

[commit-bot: I haz the power, 2016-04-26 21:11:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1918423002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1918423002/1

[commit-bot: I haz the power, 2016-04-26 21:17:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-04-26 21:18:35]

Description was changed from

==========
Fix TaskmanagerIoThreadHelper bug.

Deleting the TaskManagerIoThreadHelper should cancel any pending
OnMultipleBytesReadIO calls. If it doesn't, we can sometimes fail the
DCHECK(!bytes_read_buffer_.empty()); check.

BUG=None
TEST=TaskManagerOOPIFBrowserTest.LeavePageWithCrossSiteIframes/0
==========

to

==========
Fix TaskmanagerIoThreadHelper bug.

Deleting the TaskManagerIoThreadHelper should cancel any pending
OnMultipleBytesReadIO calls. If it doesn't, we can sometimes fail the
DCHECK(!bytes_read_buffer_.empty()); check.

BUG=None
TEST=TaskManagerOOPIFBrowserTest.LeavePageWithCrossSiteIframes/0

Committed: https://crrev.com/39b8a004d4f83d3559628b51613891d2f4773304
Cr-Commit-Position: refs/heads/master@{#389889}
==========

[commit-bot: I haz the power, 2016-04-26 21:18:36]

Patchset 1 (id:??) landed as
https://crrev.com/39b8a004d4f83d3559628b51613891d2f4773304
Cr-Commit-Position: refs/heads/master@{#389889}