Fix an AutoplayUmaHelper crash

Fix an AutoplayUmaHelper crash

There is a crash which happens when AutoplayUmaHelper receives unload
event from window, but m_element is already garbage collected. This CL
fixes this crash by making Element as a Member of AutoplayerUmaHelper.

BUG=646890
R=avayvod@chromium.org,mlamouri@chromium.org

Committed: https://crrev.com/e8cefaed4ed3209886bc4a62df0b67c6f66ece81
Cr-Commit-Position: refs/heads/master@{#418659}

[Zhiqiang Zhang (Slow), 2016-09-14 16:28:29]

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

[commit-bot: I haz the power, 2016-09-14 16:28:51]

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

[mlamouri (slow - plz ping), 2016-09-14 17:14:29]

lgtm

[commit-bot: I haz the power, 2016-09-14 20:16:57]

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

[commit-bot: I haz the power, 2016-09-14 20:16:58]

Dry run: This issue passed the CQ dry run.

[Zhiqiang Zhang (Slow), 2016-09-14 20:23:54]

The CQ bit was checked by zqzhang@chromium.org

[commit-bot: I haz the power, 2016-09-14 20:24:27]

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, 2016-09-14 20:31:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-14 20:34:10]

Description was changed from

==========
Fix an AutoplayUmaHelper crash

There is a crash which happens when AutoplayUmaHelper receives unload
event from window, but m_element is already garbage collected. This CL
fixes this crash by making Element as a Member of AutoplayerUmaHelper.

BUG=646890
R=avayvod@chromium.org,mlamouri@chromium.org
==========

to

==========
Fix an AutoplayUmaHelper crash

There is a crash which happens when AutoplayUmaHelper receives unload
event from window, but m_element is already garbage collected. This CL
fixes this crash by making Element as a Member of AutoplayerUmaHelper.

BUG=646890
R=avayvod@chromium.org,mlamouri@chromium.org

Committed: https://crrev.com/e8cefaed4ed3209886bc4a62df0b67c6f66ece81
Cr-Commit-Position: refs/heads/master@{#418659}
==========

[commit-bot: I haz the power, 2016-09-14 20:34:11]

Patchset 1 (id:??) landed as
https://crrev.com/e8cefaed4ed3209886bc4a62df0b67c6f66ece81
Cr-Commit-Position: refs/heads/master@{#418659}