Do not prematurely update position while bounds animating.

We intend to update the task size in onAnimationStart
so that we can get a new buffer as quickly as possible.
We need to keep it at the old position though, or
we will see a jump at the beginning of the animation.

Bug: 28091556
Change-Id: I5fc5f9eef1629dea88844cf3f2274eaa48909b97