Fix logic of animator start/cancel/end callbacks

The callbacks for animators in some corner cases were not being
called correctly. For example, startDelayed animators that were
started and then ended didn't send out the proper events.

This CL fixes that logic. Specifically:
- An animator that is end()'d will implicitly start() itself and then
assign an end value. This was already the case, but listeners were not
getting notified. Now this situation causes callbacks to listeners for
both the start and end events.
- startDelayed animators that are end()'d or cancel()'d prior to finishing
the startDelay phase will send out events (start and cancel/end, as appropriate)
to listeners.

Change-Id: I40a0f2fdb19d9ec7c3726a91363686c6ecb7d915