Do not create more than one ElementVisibilityObserver.

Do not create more than one ElementVisibilityObserver.

In some rare cases, we might have an ElementVisibilityObserver pending
and be back in a situation where we want to create one. In this case,
instead of creating another one, we can just skip the step.

BUG=624927
TEST=cluster-fuzz
R=zqzhang@chromium.org

Committed: https://crrev.com/53768efa825a826a9e3273b608415cea1cfd6361
Cr-Commit-Position: refs/heads/master@{#403684}

[mlamouri (slow - plz ping), 2016-07-04 14:07:49]

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

[commit-bot: I haz the power, 2016-07-04 14:08:05]

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

[Zhiqiang Zhang (Slow), 2016-07-04 14:55:02]

lgtm. Though I wonder how can the crash be triggered. Is there some bugs in
media element states?

[mlamouri (slow - plz ping), 2016-07-04 14:59:21]

On 2016/07/04 at 14:55:02, zqzhang wrote:
> lgtm. Though I wonder how can the crash be triggered. Is there some bugs in
media element states?

Some times the states are changed. For example, if you change the src. When the
callback is fired, we check back if we should play so the overhead is that we
would be listening for visibility when we could avoid it. Trying to stop
listening would be a bit of a wack a mole :)

[mlamouri (slow - plz ping), 2016-07-04 14:59:24]

The CQ bit was unchecked by mlamouri@chromium.org

[mlamouri (slow - plz ping), 2016-07-04 14:59:26]

The CQ bit was checked by mlamouri@chromium.org

[commit-bot: I haz the power, 2016-07-04 14:59:42]

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, 2016-07-04 15:30:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-04 15:30:32]

CQ bit was unchecked.

[commit-bot: I haz the power, 2016-07-04 15:31:57]

Description was changed from

==========
Do not create more than one ElementVisibilityObserver.

In some rare cases, we might have an ElementVisibilityObserver pending
and be back in a situation where we want to create one. In this case,
instead of creating another one, we can just skip the step.

BUG=624927
TEST=cluster-fuzz
R=zqzhang@chromium.org
==========

to

==========
Do not create more than one ElementVisibilityObserver.

In some rare cases, we might have an ElementVisibilityObserver pending
and be back in a situation where we want to create one. In this case,
instead of creating another one, we can just skip the step.

BUG=624927
TEST=cluster-fuzz
R=zqzhang@chromium.org

Committed: https://crrev.com/53768efa825a826a9e3273b608415cea1cfd6361
Cr-Commit-Position: refs/heads/master@{#403684}
==========

[commit-bot: I haz the power, 2016-07-04 15:31:58]

Patchset 1 (id:??) landed as
https://crrev.com/53768efa825a826a9e3273b608415cea1cfd6361
Cr-Commit-Position: refs/heads/master@{#403684}