[Custom Tab] Fix a crash when getting a screenshot of a tab

[Custom Tab] Fix a crash when getting a screenshot of a tab

Since the screenshot taking happens 1 second later than onFinishLoad(),
there should not be any guarantee of whether the tab is alive or not.

BUG=667358
Committed: https://crrev.com/3bb40d3030fd4036c4c081892e17da9f042aaa00
Cr-Commit-Position: refs/heads/master@{#433724}

[Ian Wen, 2016-11-22 00:27:42]

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

[Ian Wen, 2016-11-22 00:27:43]

PTAL

[Yusuf, 2016-11-22 00:28:02]

lgtm

[Ian Wen, 2016-11-22 00:32:49]

The CQ bit was checked by ianwen@chromium.org

[commit-bot: I haz the power, 2016-11-22 00:33:25]

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, 2016-11-22 01:10:40]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1479774769134950, "parent_rev":
"0c3a3bae0b2e13aa2f68aceeb9fc48520433c3fb", "commit_rev":
"d220bca352e9915c9f896f53d09125931c05f38e"}

[commit-bot: I haz the power, 2016-11-22 01:11:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-22 01:18:18]

Description was changed from

==========
[Custom Tab] Fix a crash when getting a screenshot of a tab

Since the screenshot taking happens 1 second later than onFinishLoad(),
there should not be any guarantee of whether the tab is alive or not.

BUG=667358
==========

to

==========
[Custom Tab] Fix a crash when getting a screenshot of a tab

Since the screenshot taking happens 1 second later than onFinishLoad(),
there should not be any guarantee of whether the tab is alive or not.

BUG=667358

Committed: https://crrev.com/3bb40d3030fd4036c4c081892e17da9f042aaa00
Cr-Commit-Position: refs/heads/master@{#433724}
==========

[commit-bot: I haz the power, 2016-11-22 01:18:18]

Patchset 1 (id:??) landed as
https://crrev.com/3bb40d3030fd4036c4c081892e17da9f042aaa00
Cr-Commit-Position: refs/heads/master@{#433724}