Clear calling identity in TransactionHangCallback

This ensures the ActivityManagerService is called with the correct
pid.

Bug: 278526360
Test: manually tested that the correct PID is sent to ActivityManager
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:705aed888b5a783d2a1f9f0392e9863afe309bdd)
Merged-In: I610014c6bc709796e9d4f7aeadf64e5107f37de3
Change-Id: I610014c6bc709796e9d4f7aeadf64e5107f37de3
1 file changed