Improve Jank for translucent activities

The previous jank improvement only worked when closing
an app, not when bringing one forward (hitting home button).
This should cover the specific case that is being missed: Having the
Home task being brought to front over a translucent window, with
a wallpaper behind both tasks.

bug:11253262
Change-Id: I200ef6fe2dda8d9ab4e1f82059b4f888c59007f4