Update client code for renegotiation.

We now need to deal with the case where a track disappears from the
labels array.

static/galene.js

@@ -349,6 +349,15 @@ function gotDownStream(c) {
     c.ondowntrack = function(track, transceiver, label, stream) {
         setMedia(c, false);
     };
+    c.onnegotiationcompleted = function() {
+        let found = false;
+        for(let key in c.labels) {
+            if(c.labels[key] === 'video')
+                found = true;
+        }
+        if(!found)
+            resetMedia(c);
+    }
     c.onstatus = function(status) {
         setMediaStatus(c);
     };
@@ -1372,6 +1381,22 @@ async function setMedia(c, isUp, mirror, video) {
     }
 }
 
+/**
+ * resetMedia resets the source stream of the media element associated
+ * with c.  This has the side-effect of resetting any frozen frames.
+ *
+ * @param {Stream} c
+ */
+function resetMedia(c) {
+    let media = /** @type {HTMLVideoElement} */
+        (document.getElementById('media-' + c.localId));
+    if(!media) {
+        console.error("Resetting unknown media element")
+        return;
+    }
+    media.srcObject = media.srcObject;
+}
+
 /**
  * @param {Element} elt
  */

static/protocol.js

@@ -622,6 +622,16 @@ ServerConnection.prototype.gotOffer = async function(id, labels, source, usernam
     }
 
     c.labelsByMid = labels;
+    c.labels = {};
+    c.pc.getTransceivers().forEach(transceiver => {
+        let label = c.labelsByMid[transceiver.mid];
+        let track = transceiver.receiver && transceiver.receiver.track;
+        if(label && track) {
+            c.labels[track.id] = label;
+        } else if(!track) {
+            console.warn("Couldn't find track for label");
+        }
+    });
     c.source = source;
     c.username = username;