Take PIP snapshot in the shell and use bounds state size for crossfading

Since the width/height of the SC should not be used anymore,
we'll use the pre-resize bounds to scale the surface before
animating the crossfade.

Bug: 186669773
Test: Enter PIP in seamless resize demo, resize with seamless
turned off uses a crossfade animation with the correct size

Change-Id: I1405be9208ac9e7cc34283e3d97dc431f0cb643c