Revert of [Blink>Media] Fix a crash in autoplay caused by delayed visibility observation

Revert of [Blink>Media] Fix a crash in autoplay caused by delayed visibility observation (patchset #1 id:1 of https://codereview.chromium.org/2671993002/ )

Reason for revert:
Decided to fix the issue in IntersectionObserver instead of HTMLMediaElement. This CL will be reverted and be superseded by the new fix.

Original issue's description:
> [Blink>Media] Fix a crash in autoplay caused by delayed visibility observation
> 
> There is a crash caused by delayed visibility observation after an
> autoplay muted video gets unmuted, so that HTMLMediaElement tries to
> stop the observer twice. However the pointer to the observer is set to
> null on stop, thus a crash happens.
> 
> This CL adds null-check in
> HTMLMediaElement::onVisibilityChangedForAutoplay() to avoid the crash.
> 
> BUG=686458
> 
> Review-Url: https://codereview.chromium.org/2671993002
> Cr-Commit-Position: refs/heads/master@{#448641}
> Committed: https://chromium.googlesource.com/chromium/src/+/0268543786283db4107d2362f338901d909545b1

TBR=mlamouri@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=686458
Review-Url: https://codereview.chromium.org/2683783002
Cr-Commit-Position: refs/heads/master@{#448727}
Committed: https://chromium.googlesource.com/chromium/src/+/a00cedc6b6caf3fdf88bba8f4dba6b6fcda64a3e

[Zhiqiang Zhang (Slow), 2017-02-07 20:45:54]

The CQ bit was checked by zqzhang@chromium.org

[Zhiqiang Zhang (Slow), 2017-02-07 20:45:55]

Created Revert of [Blink>Media] Fix a crash in autoplay caused by delayed
visibility observation

[commit-bot: I haz the power, 2017-02-07 20:47:07]

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, 2017-02-07 20:47:53]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1486500354965530, "parent_rev":
"f2da5092fa3e87ef4a0d8111f2818148238bd06c", "commit_rev":
"a00cedc6b6caf3fdf88bba8f4dba6b6fcda64a3e"}

[commit-bot: I haz the power, 2017-02-07 20:48:22]

Description was changed from

==========
Revert of [Blink>Media] Fix a crash in autoplay caused by delayed visibility
observation (patchset #1 id:1 of https://codereview.chromium.org/2671993002/ )

Reason for revert:
Decided to fix the issue in IntersectionObserver instead of HTMLMediaElement.
This CL will be reverted and be superseded by the new fix.

Original issue's description:
> [Blink>Media] Fix a crash in autoplay caused by delayed visibility observation
> 
> There is a crash caused by delayed visibility observation after an
> autoplay muted video gets unmuted, so that HTMLMediaElement tries to
> stop the observer twice. However the pointer to the observer is set to
> null on stop, thus a crash happens.
> 
> This CL adds null-check in
> HTMLMediaElement::onVisibilityChangedForAutoplay() to avoid the crash.
> 
> BUG=686458
> 
> Review-Url: https://codereview.chromium.org/2671993002
> Cr-Commit-Position: refs/heads/master@{#448641}
> Committed:
https://chromium.googlesource.com/chromium/src/+/0268543786283db4107d2362f338...

TBR=mlamouri@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=686458
==========

to

==========
Revert of [Blink>Media] Fix a crash in autoplay caused by delayed visibility
observation (patchset #1 id:1 of https://codereview.chromium.org/2671993002/ )

Reason for revert:
Decided to fix the issue in IntersectionObserver instead of HTMLMediaElement.
This CL will be reverted and be superseded by the new fix.

Original issue's description:
> [Blink>Media] Fix a crash in autoplay caused by delayed visibility observation
> 
> There is a crash caused by delayed visibility observation after an
> autoplay muted video gets unmuted, so that HTMLMediaElement tries to
> stop the observer twice. However the pointer to the observer is set to
> null on stop, thus a crash happens.
> 
> This CL adds null-check in
> HTMLMediaElement::onVisibilityChangedForAutoplay() to avoid the crash.
> 
> BUG=686458
> 
> Review-Url: https://codereview.chromium.org/2671993002
> Cr-Commit-Position: refs/heads/master@{#448641}
> Committed:
https://chromium.googlesource.com/chromium/src/+/0268543786283db4107d2362f338...

TBR=mlamouri@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=686458

Review-Url: https://codereview.chromium.org/2683783002
Cr-Commit-Position: refs/heads/master@{#448727}
Committed:
https://chromium.googlesource.com/chromium/src/+/a00cedc6b6caf3fdf88bba8f4dba...
==========

[commit-bot: I haz the power, 2017-02-07 20:48:23]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/a00cedc6b6caf3fdf88bba8f4dba...

[Zhiqiang Zhang (Slow), 2017-02-07 20:48:28]

zqzhang@chromium.org changed reviewers:
+ szager@chromium.org

[Zhiqiang Zhang (Slow), 2017-02-07 20:48:28]

+szager FYI