Validate aspect ratio if source rect hint is provided

This change simply adds a warning for the app developers and mentions
that this behavior might change in future releases.

Bug: 298529550
Bug: 326989052
Test: both log messages show for wide aspect ratio videos
Test: example of why animation is bad in those cases http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/haMvMxYpHcxiNt9gkAbGbP
Flag: none

Change-Id: I5193a1d19d86e2ec4456d1366433e7316b469e22