Mark implicit PendingIntents as immutable am: 504e7d848d am: 46387fb17b am: 78c2d2ca94 am: b0e7b88525 am: c7bb9ba897 am: e5d90630bd am: 4d38a90bf2 am: 2c7ffc65c2 am: b96576608d am: acc5340808

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12296465

Change-Id: I575d0ad39a02ee5c462395d2234083a1af045342