Support calling start() in onAnimationFinished(...) in AVD

This CL fixed an issue where calling start() from onAnimationFinished()
caused AnimationListenerBridge::onAnimationFinished(...) to be unsafely
re-entered and the new start listener was (incorrectly) reset to null.

BUG: 31971397
Test: test apk in the bug linked above
Change-Id: Ica809ef2dab884950b93b54f2d0cb4b81e9830f1