Mark navigator.mediaSession as standard (#5412)
Mark navigator.mediaSession as standard (#5412)

https://w3c.github.io/mediasession/#dom-navigator-mediasession
normatively defines navigator.mediaSession as a standard feature.
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data