Automatically trace messages on shared loopers.

There are a handful of looper threads in the system_process that
are shared by dozens of different internal services.  To help track
down what these operations are, tag the processing of each message
with a string that tries describing where it originated from: the
class name of the Handler, and the message number or class name of the
Runnable.

Bug: 28046299
Change-Id: I409ec43fea8daaae4fd70df05d4fed929a7249ae