base

Set detached wallpaper on the scale up animation.

This keeps the background wallpaper from disappearing when expanding an
app that has a wallpaper background (e.g. clock).

Fixes bug 6649988. The second half of the bug, the first half will be
reissued as a new bug.

Change-Id: I209c9038469e4133586a927c92ef64ae43fb937f