We'd like to know the proportion of HTMLMediaElement.play() calls that are
rejected due to autoplay being blocked. There are also other conditions that
cause us to reject the promise returned by HTMLMediaElement.play(), so add
telemetry to report all the identifyable conditions under which play()
succeeds or fails.
MozReview-Commit-ID: AZ67WWXaowN
--HG--
extra : rebase_source : 4a164cb0b4fb7fb6944cd371c6e90dde021a4dc0