app_list: Clear start page contents on NOTIFICATION_PROFILE_DESTROYED

app_list: Clear start page contents on NOTIFICATION_PROFILE_DESTROYED

NOTIFICATION_APP_TERMINATING could happen before closing app list bubble
on shutdown and breaks the assumption that start page contents should
out-live app list.

BUG=314567
R=mukai@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=233015

[Jun Mukai, 2013-11-04 21:42:29]

lgtm

[commit-bot: I haz the power, 2013-11-04 21:52:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/xiyuan@chromium.org/57943005/1

[commit-bot: I haz the power, 2013-11-05 02:35:44]

Retried try job too often on win_rel for step(s) content_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[commit-bot: I haz the power, 2013-11-05 03:27:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/xiyuan@chromium.org/57943005/1

[commit-bot: I haz the power, 2013-11-05 06:20:55]

Retried try job too often on linux_rel for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[xiyuan, 2013-11-05 17:18:35]

Committed patchset #1 manually as r233015 (presubmit successful).