Do not send Runnable via Messenger across processes

Instead of passing the Message#replyTo to the receiver and let receiver
post back via Messenger.

Video: http://go/recall/-/aaaaaabFQoRHlzixHdtY/cnIejHZmI9hPxzC1bjOixm
Bug: 157241292
Test: expand PiP window in secondary user
Change-Id: I276923d3508f5cce8f5c34cdcf7c11433eb8ee6b