[Extensions Toolbar] Ensure popup is closed at shutdown

[Extensions Toolbar] Ensure popup is closed at shutdown

Since the popup close process is asynchronous, it's possible that the popup
doesn't close by the time the platform delegate is deleted. If that's the
case, we need to be sure to close it, so that we do our cleanup (like
removing ourselves as an observer).

BUG=454361
Committed: https://crrev.com/30c6bd2ea49196c896dc3d43475d1a1744b529f8
Cr-Commit-Position: refs/heads/master@{#314352}

[Devlin, 2015-02-03 16:17:52]

rdevlin.cronin@chromium.org changed reviewers:
+ finnur@chromium.org

[Devlin, 2015-02-03 16:17:53]

Please take a look when you have time. :)

[Finnur, 2015-02-03 16:29:21]

LGTM

[Devlin, 2015-02-03 16:42:00]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2015-02-03 16:43:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/878813003/1

[commit-bot: I haz the power, 2015-02-03 16:46:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-03 16:47:52]

Patchset 1 (id:??) landed as
https://crrev.com/30c6bd2ea49196c896dc3d43475d1a1744b529f8
Cr-Commit-Position: refs/heads/master@{#314352}