Cheesy fix for flaky notification tests.

Posting/clearing notifications is asynchronous, so we might
need to wait (up to 200ms in this test) for them to appear
or disappear from the list returned by
getActiveNotifications().

Bug: 21930568
Change-Id: I31a88a5cdf914924e84295aaa210c0acf1a66b29
1 file changed