More targetted drawFinished fix

Prior to fe5dfcac the frameCompleteCallback
was posted to the native Looper, which is
effectively a postAtFrontOfQueue. Since it
was switched to the Java-side looper, do
an explicit postAtFrontOfQueue

Fixes: 124801988
Test: speculative
Change-Id: I287c9f3917983503402dcfe3ee7d494eefae8d1f