mash: Fix content_browser shutdown crash if ash exits at the login screen

mash: Fix content_browser shutdown crash if ash exits at the login screen

An ash crash at the login screen tears down all open windows. This can
results in the login screen's widget being destroyed before chrome shuts
down. Clean up the cached Widget/View pointers when this happens. The
chrome --mash root process will subsequently trigger a clean shutdown and
restart of content_browser.

BUG=691134
TEST=for classic ash, existing chromeos login tests. For mash, trigger ash
crash at login screen and observe browser shut down cleanly.

Review-Url: https://codereview.chromium.org/2690283002
Cr-Commit-Position: refs/heads/master@{#450179}
Committed: https://chromium.googlesource.com/chromium/src/+/b54401a5a1107d8440ddad54effecca920553fa6

[James Cook, 2017-02-13 23:11:21]

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

[commit-bot: I haz the power, 2017-02-13 23:12:28]

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

[James Cook, 2017-02-13 23:12:29]

jamescook@chromium.org changed reviewers:
+ sky@chromium.org

[James Cook, 2017-02-13 23:12:29]

sky, please take a look. This is the simplest fix and doesn't involve any
special wiring into shutdown or MusClient.

[James Cook, 2017-02-13 23:22:06]

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

[commit-bot: I haz the power, 2017-02-13 23:22:55]

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

[sky, 2017-02-13 23:46:31]

LGTM

[James Cook, 2017-02-13 23:49:43]

The CQ bit was unchecked by jamescook@chromium.org

[James Cook, 2017-02-13 23:49:48]

The CQ bit was checked by jamescook@chromium.org

[commit-bot: I haz the power, 2017-02-13 23:50:17]

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, 2017-02-14 00:57:49]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1487029788303080,
"parent_rev": "518d37c3c167ec8f0a790a4eda037b6e643ebc8f", "commit_rev":
"b54401a5a1107d8440ddad54effecca920553fa6"}

[commit-bot: I haz the power, 2017-02-14 00:58:26]

Description was changed from

==========
mash: Fix content_browser shutdown crash if ash exits at the login screen

An ash crash at the login screen tears down all open windows. This can
results in the login screen's widget being destroyed before chrome shuts
down. Clean up the cached Widget/View pointers when this happens. The
chrome --mash root process will subsequently trigger a clean shutdown and
restart of content_browser.

BUG=691134
TEST=for classic ash, existing chromeos login tests. For mash, trigger ash
crash at login screen and observe browser shut down cleanly.
==========

to

==========
mash: Fix content_browser shutdown crash if ash exits at the login screen

An ash crash at the login screen tears down all open windows. This can
results in the login screen's widget being destroyed before chrome shuts
down. Clean up the cached Widget/View pointers when this happens. The
chrome --mash root process will subsequently trigger a clean shutdown and
restart of content_browser.

BUG=691134
TEST=for classic ash, existing chromeos login tests. For mash, trigger ash
crash at login screen and observe browser shut down cleanly.

Review-Url: https://codereview.chromium.org/2690283002
Cr-Commit-Position: refs/heads/master@{#450179}
Committed:
https://chromium.googlesource.com/chromium/src/+/b54401a5a1107d8440ddad54effe...
==========

[commit-bot: I haz the power, 2017-02-14 00:58:27]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/b54401a5a1107d8440ddad54effe...