Fade to empty view when no tasks for Recents Go

This CL adds a view for when there are no tasks and fades into/out of it
appropriately based off changes to the adapter.

Bug: 114136250
Test: Add task, remove task, see empty view shows up properly.
Change-Id: I47d0bbfb19d56f5f0de5bec3c0ac2b5cfb63253f
2 files changed