DO NOT MERGE Reset top focused root task when task hidden

The focused app was not updated when bubble minimized and causing
ANR.

Bug: 179676966
Bug: 171522827
Test: expand and minimize bubbles
Test: 1) play video
      2) adjust volume
      3) get bubble, expand it, adjust volume
      4) collapse bubble
      5) adjust volume
      => Should see volume dialog; no ANR
Change-Id: If04de21b954d074b045e76d7d23e02dade60cdbe
(cherry picked from commit a782799b)