Reduce memory churn from main thread looper tracing

Implement getTraceName() on two top Handlers on
the main thread Looper to avoid calls to getClass().getName()

Also avoids posting to main thread handler from the same thread in
FrameTracker callback

Bug: 285737625
Test: Manual - collect a trace and confirm main thread slice names
Change-Id: I7dbbd7702e339e8cf3e7c42d4df3762250e5aca5