Force uniform width for MATCH_PARENT in AlertDialogLayout

The initial layout passes run using whatever was specified by the
parent, which ensures that TOO_SMALL will get set correctly when
needed. The final layout pass runs as EXACTLY to ensure that
MATCH_PARENT widths are correctly set.

Bug: 27030200
Change-Id: Ia7af3f75746e725761e78e7c4eefb0b31f499113