feat(JingleSessionPC): add options for P2P evaluation

Add 'forceJVB121Ratio' config option which allows to enforce JVB
conference even if the P2P connection can be established. In such case
'forceJVB121' permanent analytics property will be added.

Will also set 'p2pFailed' analytics property to 'true' in case ICE fails
on the P2P connection.

JitsiConference.js

  * @param {number} [options.config.channelLastN=-1] The requested amount of
  * videos are going to be delivered after the value is in effect. Set to -1 for
  * unlimited or all available videos.
+ * @param {number} [options.config.forceJVB121Ratio]
+ * "Math.random() < forceJVB121Ratio" will determine whether a 2 people
+ * conference should be moved to the JVB instead of P2P. The decision is made on
+ * the responder side, after ICE succeeds on the P2P connection.
  * @constructor
  *
  * FIXME Make all methods which are called from lib-internal classes
         // Let the RTC service do any cleanups
         this.rtc.onCallEnded();
     } else if (jingleSession === this.p2pJingleSession) {
+        // It's the responder who decides to enforce JVB mode, so that both
+        // initiator and responder are aware if it was intentional.
+        if (reasonCondition === 'decline' && reasonText === 'force JVB121') {
+            logger.info('In forced JVB 121 mode...');
+            Statistics.analytics.addPermanentProperties({ forceJvb121: true });
+        } else if (reasonCondition === 'connectivity-error'
+            && reasonText === 'ICE FAILED') {
+            // It can happen that the other peer detects ICE failed and
+            // terminates the session, before we get the event on our side.
+            // But we are able to parse the reason and mark it here.
+            Statistics.analytics.addPermanentProperties({ p2pFailed: true });
+        }
         this._stopP2PSession();
     } else {
         logger.error(
     // We do nothing for the JVB connection, because it's up to the Jicofo to
     // eventually come up with the new offer (at least for the time being).
     if (session.isP2P) {
+        // Add p2pFailed property to analytics to distinguish, between "good"
+        // and "bad" connection
+        Statistics.analytics.addPermanentProperties({ p2pFailed: true });
+
+        // Log analytics event, but only for the initiator to not count it twice
         if (this.p2pJingleSession && this.p2pJingleSession.isInitiator) {
             Statistics.sendEventToAll('p2p.failed');
         }
  */
 JitsiConference.prototype._onIceConnectionEstablished
 = function(jingleSession) {
+    const forceJVB121Ratio = this.options.config.forceJVB121Ratio;
+
     // We don't care about the JVB case, there's nothing to be done
     if (!jingleSession.isP2P) {
         return;
     } else if (this.p2pJingleSession !== jingleSession) {
         logger.error('CONNECTION_ESTABLISHED - wrong P2P session instance ?!');
 
+        return;
+    } else if (!jingleSession.isInitiator
+        && typeof forceJVB121Ratio === 'number'
+        && Math.random() < forceJVB121Ratio) {
+        logger.info(`Forcing JVB 121 mode (ratio=${forceJVB121Ratio})...`);
+        this._rejectIncomingCall(
+            jingleSession, {
+                reasonTag: 'decline',
+                reasonMsg: 'force JVB121'
+            });
+        Statistics.analytics.addPermanentProperties({ forceJvb121: true });
+
         return;
     }
 
     if (newStatus) {
         logger.info('Peer to peer connection established!');
 
+        // When we end up in a valid P2P session need to reset the properties
+        // in case they have persisted, after session with another peer.
+        Statistics.analytics.addPermanentProperties({
+            p2pFailed: false,
+            forceJvb121: false
+        });
+
         // Sync up video transfer active in case p2pJingleSession not existed
         // when the lastN value was being adjusted.
         const isVideoActive = this.rtc.getLastN() !== 0;