Currently, when starting another video, media controls are transfered to the new player. If the player goes away (tab closed, navigate away, etc) media controls are disabled. This patch makes it keep track of all players that were playing and transfers control to the previous player instead.
Also have "stop" do the same if there's another player available.

Started watching a video, opened a video in a second tab, closed that tab, controlled previous player again.
Verified it didn't resume the previous video if it was paused.