commit 1abb683a66d12c6487cd3fd0afa61469dc7341f3
author Yunfan Chen <yunfanc@google.com> Wed Oct 30 11:44:29 2019 -0700
committer Yunfan Chen <yunfanc@google.com> Wed Oct 30 11:45:57 2019 -0700
tree 48acf396d01ca06215182f250dcb89934cc7b9fb
parent 4a0b1750ef697bb4f329a3beffe88bf46e1e6385

Notify task description change to system UI (4/N)

The TaskStackChangeListener will take the task description chagne event
and notify the listeners. It will be able to let system UI handle the
theme change of the task correctly.

Bug: 113253712
Bug: 122726344
Test: go/wm-smoke
Test: Test with an app with theme, the listener will receive the
      background color.
Test: Manually registered a listener from system UI and the event is
      correctly received.

Change-Id: I087cc112be73cf421fa124cd0d6b238f91970a0c