Prevent updating aspect ratio unless it is different.

- The old check of the bounds assumed there was no expanded state, so when
  a PiP activity tries to set the aspect ratio from a a menu action, it
  will cause an animation to the normal bounds again.

Bug: 36462497
Test: Set aspect ratio in pip action handler
Change-Id: Iba5e9571a3024c8369c2a24d32c2d8f34831ede4