Cache locations of where nearest child is.

Computing the full tap area of a child/button helps
determine which regions launcher avoids starting the recents
animation for (ex. tapping over back button).
Previously we were only sending a button view's bounds
instead of the tappable region outside those bounds.

bug: 165805948
Test: Modifying existing tests in-progress.
Repro steps from bug no longer repro.

Change-Id: Icf11a0cf3de5b563b265c21f04afc13ea264f75b