Don't notify updates while initializing AnimatorSet

Fixes: 269785397

When an AnimatorSet runs, it should not call
onAnimationUpdate() during initialization.

Test: new test
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:90eabef83b63d42f73233a9c025850999f0d8175)
Merged-In: Ic53d346b17c06a8d9ae9af8c28681dd84cc630fc
Change-Id: Ic53d346b17c06a8d9ae9af8c28681dd84cc630fc