Add synchronized locks to bugreport callback methods

BugreportCallbackImpl class methods modify (read/write) the private
variable mInfo. Add synchronized locks for consistency.

Make other methods static to be thread-safe, and operate only on its
arguments.

Bug: 123617758
Test: Build and flash. Takes bugreport as expected
Change-Id: I237fd940f5ccd4833d053558cf1b014883d59791