Update mEndRect when closing ArrowPopup

Generally mEndRect is still correct from when we set it in
animateOpen(), but there are cases where it is no longer valid and
should be recomputed in animateClose(). For example, if you dismiss
notifications, the height of the popup changes between opening and
closing it.

Test: Long press an icon with a notification dot, dismiss all
notifications from the popup and then close the popup. The shadow
follows the outline of the popup, instead of extending well below it.

Change-Id: Ic5d6ad2807ea1ec8aff5e3d6ce8abaa11ce5d33c