e2ee: update for latest spec changes in Chrome M84

which landed in
  https://bugs.chromium.org/p/chromium/issues/detail?id=1069295#c4

modules/browser/BrowserCapabilities.js

      */
     supportsInsertableStreams() {
         return Boolean(typeof window.RTCRtpSender !== 'undefined'
-            && window.RTCRtpSender.prototype.createEncodedVideoStreams);
+            && (window.RTCRtpSender.prototype.createEncodedStreams
+                || window.RTCRtpSender.prototype.createEncodedVideoStreams));
     }
 
     /**

modules/e2ee/E2EEContext.js

         }
         receiver[kJitsiE2EE] = true;
 
-        const receiverStreams
-            = kind === 'video' ? receiver.createEncodedVideoStreams() : receiver.createEncodedAudioStreams();
+        let receiverStreams;
+
+        if (receiver.createEncodedStreams) {
+            receiverStreams = receiver.createEncodedStreams();
+        } else {
+            receiverStreams = kind === 'video' ? receiver.createEncodedVideoStreams()
+                : receiver.createEncodedAudioStreams();
+        }
 
         this._worker.postMessage({
             operation: 'decode',
         }
         sender[kJitsiE2EE] = true;
 
-        const senderStreams
-            = kind === 'video' ? sender.createEncodedVideoStreams() : sender.createEncodedAudioStreams();
+        let senderStreams;
+
+        if (sender.createEncodedStreams) {
+            senderStreams = sender.createEncodedStreams();
+        } else {
+            senderStreams = kind === 'video' ? sender.createEncodedVideoStreams()
+                : sender.createEncodedAudioStreams();
+        }
 
         this._worker.postMessage({
             operation: 'encode',

modules/e2ee/Worker.js

 // Worker for E2EE/Insertable streams. Currently served as an inline blob.
 const code = `
+    // Polyfill RTCEncoded(Audio|Video)Frame.getMetadata() (not available in M83, available M84+).
+    // The polyfill can not be done on the prototype since its not exposed in workers. Instead,
+    // it is done as another transformation to keep it separate.
+    function polyFillEncodedFrameMetadata(encodedFrame, controller) {
+      if (!encodedFrame.getMetadata) {
+        encodedFrame.getMetadata = function() {
+          return {
+            // TODO: provide a more complete polyfill based on additionalData for video.
+            synchronizationSource: this.synchronizationSource,
+            contributingSources: this.contributingSources
+          };
+        };
+      }
+      controller.enqueue(encodedFrame);
+    }
+
     // We use a ringbuffer of keys so we can change them and still decode packets that were
     // encrypted with an old key.
     // In the future when we dont rely on a globally shared key we will actually use it. For
             const keyIndex = this._currentKeyIndex % this._cryptoKeyRing.length;
 
             if (this._cryptoKeyRing[keyIndex]) {
-                const iv = this.makeIV(encodedFrame.synchronizationSource, encodedFrame.timestamp);
+                const iv = this.makeIV(encodedFrame.getMetadata().synchronizationSource, encodedFrame.timestamp);
 
                 return crypto.subtle.encrypt({
                     name: 'AES-GCM',
             });
 
             readableStream
+                .pipeThrough(new TransformStream({
+                  transform: polyFillEncodedFrameMetadata, // M83 polyfill.
+                }))
                 .pipeThrough(transformStream)
                 .pipeTo(writableStream);
             if (keyBytes) {
             });
 
             readableStream
+                .pipeThrough(new TransformStream({
+                  transform: polyFillEncodedFrameMetadata, // M83 polyfill.
+                }))
                 .pipeThrough(transformStream)
                 .pipeTo(writableStream);
             if (keyBytes) {