These event names: macro(webkitsourceclose) \ macro(webkitsourceended) \ macro(webkitsourceopen) \ were added in https://trac.webkit.org/changeset/117662/webkit but don't appear to be used any more.
can go away, we have official event name now. sourceopen sourceended sourceclose https://www.w3.org/TR/media-source/#dfn-sourceopen
We don't need to support the webkit-prefixed names?
<rdar://problem/85945878>