The factory methods for creating the Media* nodes are currently defined on the BaseAudioContext. This is incorrect. They should only be defined on an AudioContext.
This is a legacy issue from the time before there was a BaseAudioContext. Also, we didn't have any way of running tests on trybots because they may not have audio HW, so we used an OfflineAudioContext.
This latter issue is fixed (https://chromium-review.googlesource.com/c/chromium/src/+/1067100) so we can use an AudioContext now.
Comment 1 by rtoy@chromium.org
, May 23 2018