Address flakes in BubbleBarViewAnimatorTest

 - Fix some mockito issue by using a fake implementation rather
   than a mock.
 - Return early in the bubble bar animation if there's no animating
   bubble. The issue here is that the scaleY property of the bubble
   bar is set to 1 when the animation is interrupted. However, in
   the test environment, the cancellation of the animator is posted
   to a different thread, and another animation frame is running
   after the scaleY was already reset to 1.

Flag: EXEMPT test only
Test: atest BubbleBarViewAnimatorTest
Bug: 399934422
Bug: 399720438
Change-Id: I271f670c50168237aeaf867c8171ae3023ee09ff