Calculate outset hint when adding window.

Outsets aren't dynamic so they are a great candidate for a hint when the
window is added through the window manager. Thanks to this during first
view hierarchy measure or wallpaper window layout they are immediately
available and don't require multiple measure/layout passes.

Bug: 21593814
Change-Id: I573c15ffbbe4fcd8a6ed9c5e4fcd6cfbbcd7434f