Floating window: Fix possible NPE

Avoid possible NPE if app provides no interface such as pushbullet's
test notification & other apps which provide one.
PackageManagerService: Fix concurrent access to shared state

Stop multiple threads from all calling add on the same HashMap.

Cleanup the use of a boolean flag by removing concurrent writes
to it.

Change-Id: I8d61fe7294dcb67ee7d0d7de88d90d2051c310e6
Merge remote-tracking branch 'PA/kitkat' into kitkat-staging