Use PendingIntent.FLAG_IMMUTABLE in PendingIntent in NotificationMgr

Require that the PendingIntent be immutable so that a malicious app is
 not able to hijack and mutate any of the details.

Test: Android builds
Bug: 153356561
Change-Id: Ib278926f4327b3fcbec25795b78643774911d1dc
Merged-In: Ib278926f4327b3fcbec25795b78643774911d1dc
1 file changed