Keep app when opening floating window from recents panel

Start activity asynchronously by appending it to system's
message queue to let RecentsPanelView cleanly execute
dismissAndGoBack before the floating window gets started.

Change-Id: Ie9c74b9f0b39f3aee81c62246cdcae15de83ee0d
Merge "Keep app when opening floating window from recents panel" into kitkat