Revert "Replace onTaskMovedToFront with a transition observer in bubbles"

This reverts commit 3fdcd275ff10798ef06cadd6f68995b5179f2ddb.

Reason for revert:  Potential culprit for b/297936285 - verifying through ABTD before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted

Change-Id: I6ebdddcc132ffe04e5fda5bfdaee4a59b2e12bd8
6 files changed