ref(JingleSessionPC): send source update upon reconnect

Given that the XMPP connection is able to reconnect after a drop, now
the jingle session needs to hold off any updates that have to be sent
while the signalling is down. Send the update upon reconnect to sync
Jicofo and JVB with the client's source description.

modules/xmpp/JingleSessionPC.js

 import XMPPEvents from '../../service/xmpp/XMPPEvents';
 import AsyncQueue from '../util/AsyncQueue';
 import GlobalOnErrorHandler from '../util/GlobalOnErrorHandler';
+import XmppConnection from './XmppConnection';
 
 const logger = getLogger(__filename);
 
          */
         this._bridgeSessionId = null;
 
+        /**
+         * The oldest SDP passed to {@link notifyMySSRCUpdate} while the XMPP connection was offline that will be
+         * used to update Jicofo once the XMPP connection goes back online.
+         * @type {SDP|undefined}
+         * @private
+         */
+        this._cachedOldLocalSdp = undefined;
+
+        /**
+         * The latest SDP passed to {@link notifyMySSRCUpdate} while the XMPP connection was offline that will be
+         * used to update Jicofo once the XMPP connection goes back online.
+         * @type {SDP|undefined}
+         * @private
+         */
+        this._cachedNewLocalSdp = undefined;
+
         /**
          * Stores result of {@link window.performance.now()} at the time when
          * ICE enters 'checking' state.
          * @type {number}
          */
         this.establishmentDuration = undefined;
+
+        this._xmppListeners = [];
+        this._xmppListeners.push(
+            connection.addEventListener(
+                XmppConnection.Events.CONN_STATUS_CHANGED,
+                this.onXmppStatusChanged.bind(this))
+        );
     }
 
     /* eslint-enable max-params */
         // this.reasonText = reasonText;
         logger.info(`Session terminated ${this}`, reasonCondition, reasonText);
 
+        this._xmppListeners.forEach(removeListener => removeListener());
+        this._xmppListeners = [];
+
         this.close();
     }
 
+    /**
+     * Handles XMPP connection state changes.
+     *
+     * @param {XmppConnection.Status} status - The new status.
+     */
+    onXmppStatusChanged(status) {
+        if (status === XmppConnection.Status.CONNECTED && this._cachedOldLocalSdp) {
+            logger.info('Sending SSRC update on reconnect');
+            this.notifyMySSRCUpdate(
+                this._cachedOldLocalSdp,
+                this._cachedNewLocalSdp);
+        }
+    }
+
     /**
      * Parse the information from the xml sourceAddElem and translate it
      *  into sdp lines
             return;
         }
 
+        if (!this.connection.connected) {
+            // The goal is to compare the oldest SDP with the latest one upon reconnect
+            if (!this._cachedOldLocalSdp) {
+                this._cachedOldLocalSdp = oldSDP;
+            }
+            this._cachedNewLocalSdp = newSDP;
+            logger.warn('Not sending SSRC update while the signaling is disconnected');
+
+            return;
+        }
+
+        this._cachedOldLocalSdp = undefined;
+        this._cachedNewLocalSdp = undefined;
+
         // send source-remove IQ.
         let sdpDiffer = new SDPDiffer(newSDP, oldSDP);
         const remove = $iq({ to: this.remoteJid,