[CCT-Reparenting] Remove tab observer when the tab is removed from model

[CCT-Reparenting] Remove tab observer when the tab is removed from model

In tab reparenting, we never close but only remove the tab from the
model. During this process, both tab observer and also the metrics
observer was still kept, which leaked over some custom tab features into
the tab even after it was reparented. This removes the observers and
fixes the related issues.

TEST=CustomTabActivityTest#testTabReparentingBasic
BUG=669169
Committed: https://crrev.com/7810c370957e89c47198cb52e3bd09d03193f956
Cr-Commit-Position: refs/heads/master@{#435028}

[Yusuf, 2016-11-29 00:34:53]

yusufo@chromium.org changed reviewers:
+ ianwen@chromium.org

[Ian Wen, 2016-11-29 00:37:38]

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

[commit-bot: I haz the power, 2016-11-29 00:38:25]

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

[Ian Wen, 2016-11-29 00:39:24]

lgtm

[commit-bot: I haz the power, 2016-11-29 02:36:47]

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

[commit-bot: I haz the power, 2016-11-29 02:36:48]

Dry run: This issue passed the CQ dry run.

[Yusuf, 2016-11-29 17:50:58]

The CQ bit was checked by yusufo@chromium.org

[commit-bot: I haz the power, 2016-11-29 17:51:15]

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, 2016-11-29 17:55:59]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1480441858779810, "parent_rev":
"eac2cf6536d923616784629e6c177a7a64fbc38d", "commit_rev":
"39a2c72f2ccecfa50e249d489388d91d7ada0545"}

[commit-bot: I haz the power, 2016-11-29 17:56:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-29 17:59:04]

Description was changed from

==========
[CCT-Reparenting] Remove tab observer when the tab is removed from model

In tab reparenting, we never close but only remove the tab from the
model. During this process, both tab observer and also the metrics
observer was still kept, which leaked over some custom tab features into
the tab even after it was reparented. This removes the observers and
fixes the related issues.

TEST=CustomTabActivityTest#testTabReparentingBasic
BUG=669169
==========

to

==========
[CCT-Reparenting] Remove tab observer when the tab is removed from model

In tab reparenting, we never close but only remove the tab from the
model. During this process, both tab observer and also the metrics
observer was still kept, which leaked over some custom tab features into
the tab even after it was reparented. This removes the observers and
fixes the related issues.

TEST=CustomTabActivityTest#testTabReparentingBasic
BUG=669169

Committed: https://crrev.com/7810c370957e89c47198cb52e3bd09d03193f956
Cr-Commit-Position: refs/heads/master@{#435028}
==========

[commit-bot: I haz the power, 2016-11-29 17:59:04]

Patchset 1 (id:??) landed as
https://crrev.com/7810c370957e89c47198cb52e3bd09d03193f956
Cr-Commit-Position: refs/heads/master@{#435028}