Dispatch "addtrack" and "removetrack" events in MediaStream shim

Neither Firefox nor Chromium dispatch "addtrack" and "removetrack"
events when tracks are added and removed to and from a MediaStream.
However, this is part of the specification, so it is expected that all
browsers implement that eventually. Due to that the shim checks whether
the events were dispatched or not in order to do it only when needed.

Signed-off-by: Daniel Calviño Sánchez <[email protected]>

src/utils/webrtc/shims/MediaStream.js

@@ -20,6 +20,40 @@
  */
 
 if (window.MediaStream) {
+	const originalMediaStreamAddTrack = window.MediaStream.prototype.addTrack
+	window.MediaStream.prototype.addTrack = function(track) {
+		let addTrackEventDispatched = false
+		const testAddTrackEvent = () => {
+			addTrackEventDispatched = true
+		}
+		this.addEventListener('addtrack', testAddTrackEvent)
+
+		originalMediaStreamAddTrack.apply(this, arguments)
+
+		this.removeEventListener('addtrack', testAddTrackEvent)
+
+		if (!addTrackEventDispatched) {
+			this.dispatchEvent(new MediaStreamTrackEvent('addtrack', { track: track }))
+		}
+	}
+
+	const originalMediaStreamRemoveTrack = window.MediaStream.prototype.removeTrack
+	window.MediaStream.prototype.removeTrack = function(track) {
+		let removeTrackEventDispatched = false
+		const testRemoveTrackEvent = () => {
+			removeTrackEventDispatched = true
+		}
+		this.addEventListener('removetrack', testRemoveTrackEvent)
+
+		originalMediaStreamRemoveTrack.apply(this, arguments)
+
+		this.removeEventListener('removetrack', testRemoveTrackEvent)
+
+		if (!removeTrackEventDispatched) {
+			this.dispatchEvent(new MediaStreamTrackEvent('removetrack', { track: track }))
+		}
+	}
+
 	// Event implementations do not support advanced parameters like "options"
 	// or "useCapture".
 	const originalMediaStreamDispatchEvent = window.MediaStream.prototype.dispatchEvent