Convert mHistory to mTaskHistory (6)

- Convert isInStackLocked from mHistory to mTaskHistory.
- Fix discrepancy between mHistory and mTaskHistory when all
activities in a task are finishing and a new one is being added.
mHistory was separating the task into two places in the stack,
mTaskHistory can't do that.
- Convert startActivityUncheckedLocked from mHistory to mTaskHistory.
- Convert finishTopRunningActivityLocked from mHistory to mTaskHistory.

Change-Id: I42b097c2f187d40ecd98b108794757063903218b