bc571a9807
This will remove the need for having all the null checks in TaskStackView. We also remove the check when launching tasks (the fail case is worse when the activity fails to load). And the CL also fix the header focus animation, and an issue with tasks not getting laid out when the stack is set again. Change-Id: I9b4cd50d76f72ba3d16dd1b8e2d9bbf9f1f24d2b