Avoid waiting from polling binder threads

It's not enough to test whether we're the only looper thread.  In the
case of a polling binder implementation, there is still only one thread
able to handle callbacks.  That thread will also have to fall back to
the inefficient check-and-recheck method rather than waiting.

As such, ask whether we're the sole binder thread instead.

Bug: 71625413
Test: start a polling hwbinder service (e.g. healthd@2.0/backup) before
      its dependency; doesn't hang.
Change-Id: Ie2ae4f5705aba17f20227f1e1a58341d4da13fe1
1 file changed