Animates a fake TaskView in Home gesture tutorial.

The "TaskView" morphs as you drag up from the
nav bar, and transforms into a "home icon" or
final "TaskView" when you release your finger.

If you cancel the gesture (e.g. drag back down),
the view simply fades out and provides a hint
to swipe straight up.

Demo: https://drive.google.com/open?id=1NXlO1W6IhLoX0k2K6b-QZ5IXp0o7OYqO

Bug: 148542211
Change-Id: I3d5e9a45fcadc6a498941ea17813b9487720a504