Reduce FAB padding and FAB size in concert for multiwindow

Bug: 26840878

The support library implementation of the FAB automatically
reduces the FAB size when both width and height shrink below
470dp (on L+). To reclaim more vertical space, Clock now also
shrinks the padding around the fab at the same time.

Change-Id: Ic5a4452463f4979c5b309877450aae50975deb14