[ios] Fix WebStateListFastEnumerationHelper observer unregistration.

[ios] Fix WebStateListFastEnumerationHelper observer unregistration.

Convert WebStateListFastEnumerationHelper to use RAII to automatically
unregister the WebStateListObserver from the WebStateList observer list.

BUG=712391
Review-Url: https://codereview.chromium.org/2819373004
Cr-Commit-Position: refs/heads/master@{#465572}
Committed: https://chromium.googlesource.com/chromium/src/+/4a0a4e85d2a8d23a9aeb528bec0dac702b43c5f6

[sdefresne, 2017-04-18 17:00:10]

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

[commit-bot: I haz the power, 2017-04-18 17:00:37]

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

[sdefresne, 2017-04-18 17:00:39]

sdefresne@chromium.org changed reviewers:
+ rohitrao@chromium.org

[sdefresne, 2017-04-18 17:00:39]

Please take a look and send to CQ if LGTY.

[commit-bot: I haz the power, 2017-04-18 17:13:28]

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

[commit-bot: I haz the power, 2017-04-18 17:13:29]

Dry run: This issue passed the CQ dry run.

[rohitrao (ping after 24h), 2017-04-19 11:28:48]

lgtm

[sdefresne, 2017-04-19 13:10:52]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2017-04-19 13:11:14]

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, 2017-04-19 13:16:17]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1492607452711040, "parent_rev":
"80b7800cb1db49464afa64d370c09c7f65251dca", "commit_rev":
"4a0a4e85d2a8d23a9aeb528bec0dac702b43c5f6"}

[commit-bot: I haz the power, 2017-04-19 13:16:25]

Description was changed from

==========
[ios] Fix WebStateListFastEnumerationHelper observer unregistration.

Convert WebStateListFastEnumerationHelper to use RAII to automatically
unregister the WebStateListObserver from the WebStateList observer list.

BUG=712391
==========

to

==========
[ios] Fix WebStateListFastEnumerationHelper observer unregistration.

Convert WebStateListFastEnumerationHelper to use RAII to automatically
unregister the WebStateListObserver from the WebStateList observer list.

BUG=712391

Review-Url: https://codereview.chromium.org/2819373004
Cr-Commit-Position: refs/heads/master@{#465572}
Committed:
https://chromium.googlesource.com/chromium/src/+/4a0a4e85d2a8d23a9aeb528bec0d...
==========

[commit-bot: I haz the power, 2017-04-19 13:16:26]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/4a0a4e85d2a8d23a9aeb528bec0d...