- Introduce the task history and add to and remove from it with verification. Change-Id: If97e74f5a13f85acdb1521fc6d0b066a7e8584ae
- Add/remove/move TaskLists from ActivityStack. - Further isolate mHistory. - Cleanup warnings by parameterizing ArrayList. - Fix previous bugs. Change-Id: Ife8c7b7347479c70f10467cc384283456149ac50