Fix the same active time tasks disappeared on RunngintTasks

In |getTasks|, a TreeSet is used to sort task by last active time
directly. However, the TreeSet is no duplicatable, so the if the
comparing task have the same lastActiveTime, one of them will be
dropped.

This CL add task id as the extra field on comparator.

Bug: 191729305
Test: manually launch many apps.
Change-Id: Iee39e438224f3ef22bc0a9254be88eec842c61a6