PopupWidget: Toggle clipping -after- updating dimensions

ClippableElement#toggleClipping no longer clips asynchronously (I60742642), so we need to call it
after we've set the dimensions.

Bug: 70423
Change-Id: I1a6fda4091bc9b35eb28cf4832095d0bb1565f05
(cherry picked from commit 720debe43c9f77b5e8e1c3de0bf4f07d1068f8c9)