Cherrypick d1ed33c4 from hc-mr1. do not merge.

Fix zombie threads in the Layoutlib.

Some widgets can create (indirectly) HandlerThread which are started
but never stopped.

This patch use the delegate methods to override the thread run method
to record which threads are started to be able to call quit() on them
after a render.

Note that we should really fix layoutlib_create to be able to call
the default implementation from a delegate to remove code duplication.

Change-Id: Iaf5432623e9704bb3114a8e0583c8553282c205e