Fix stream end/start race condition

We need to queue attempts to call modifySources to prevent errors in
setLocalDescription, et al. We need to let the asynchronous function
flow in modifySources finish before we kick off another set.

modules/xmpp/JingleSession.js

 var SDPUtil = require("./SDPUtil");
 var SDP = require("./SDP");
 var RTCBrowserType = require("../../service/RTC/RTCBrowserType");
+var async = require("async");
 
 // Jingle stuff
 function JingleSession(me, sid, connection, service) {
      * by the application logic.
      */
     this.videoMuteByUser = false;
+    this.modifySourcesQueue = async.queue(this._modifySources.bind(this), 1);
 }
 
 //TODO: this array must be removed when firefox implement multistream support
         });
         sdp.raw = sdp.session + sdp.media.join('');
     });
-    this.modifySources();
+    this.modifySourcesQueue.push();
 };
 
 JingleSession.prototype.removeSource = function (elem, fromJid) {
         });
         sdp.raw = sdp.session + sdp.media.join('');
     });
-    this.modifySources();
+    this.modifySourcesQueue.push();
 };
 
-JingleSession.prototype.modifySources = function (successCallback) {
+JingleSession.prototype._modifySources = function (successCallback, queueCallback) {
     var self = this;
+
     if (this.peerconnection.signalingState == 'closed') return;
     if (!(this.addssrc.length || this.removessrc.length || this.pendingop !== null || this.switchstreams)){
         // There is nothing to do since scheduled job might have been executed by another succeeding call
         if(successCallback){
             successCallback();
         }
-        return;
-    }
-
-    // FIXME: this is a big hack
-    // https://code.google.com/p/webrtc/issues/detail?id=2688
-    // ^ has been fixed.
-    if (!(this.peerconnection.signalingState == 'stable' && this.peerconnection.iceConnectionState == 'connected')) {
-        console.warn('modifySources not yet', this.peerconnection.signalingState, this.peerconnection.iceConnectionState);
-        this.wait = true;
-        window.setTimeout(function() { self.modifySources(successCallback); }, 250);
-        return;
-    }
-    if (this.wait) {
-        window.setTimeout(function() { self.modifySources(successCallback); }, 2500);
-        this.wait = false;
+        queueCallback();
         return;
     }
 
 
             if(self.signalingState == 'closed') {
                 console.error("createAnswer attempt on closed state");
+                queueCallback("createAnswer attempt on closed state");
                 return;
             }
 
                             if(successCallback){
                                 successCallback();
                             }
+                            queueCallback();
                         },
                         function(error) {
                             console.error('modified setLocalDescription failed', error);
+                            queueCallback(error);
                         }
                     );
                 },
                 function(error) {
                     console.error('modified answer failed', error);
+                    queueCallback(error);
                 }
             );
         },
         function(error) {
             console.error('modify failed', error);
+            queueCallback(error);
         }
     );
 };
 
+
 /**
  * Switches video streams.
  * @param new_stream new stream that will be used as video of this session.
     }
 
     self.switchstreams = true;
-    self.modifySources(function() {
+    self.modifySourcesQueue.push(function() {
         console.log('modify sources done');
 
         success_callback();
 
     this.hardMuteVideo(mute);
 
-    this.modifySources(callback(mute));
+    this.modifySourcesQueue.push(callback(mute));
 };
 
 JingleSession.prototype.hardMuteVideo = function (muted) {

package.json

       "pako": "*",
       "i18next-client": "1.7.7",
       "sdp-interop": "jitsi/sdp-interop#f65fedfe57a",
-      "sdp-transform": "1.3.0"
+      "sdp-transform": "1.3.0",
+      "async": "0.9.0"
   },
   "devDependencies": {
   },