Updating scalable default in MediaSizeWidget

Updating defaults when scalable is attached to media size widget.
This makes sure the defaults are loaded initially; they will change
later by the scalable default change event.

h/t Roan for figuring this out.

Change-Id: Ie45419a9f88694484d072dbc28d451fdc0ba06c1
Merge "Updating scalable default in MediaSizeWidget"