fix(stats) Emit stats using source name as key (#1996)

This allows us to display resolution and framerate stats on separate tiles when multi-stream mode is enabled.

modules/statistics/RTPStatsCollector.js

 import { MediaType } from '../../service/RTC/MediaType';
 import * as StatisticsEvents from '../../service/statistics/Events';
 import browser from '../browser';
+import FeatureFlags from '../flags/FeatureFlags';
 
 const GlobalOnErrorHandler = require('../util/GlobalOnErrorHandler');
 
                 videoCodec = ssrcStats.codec;
             }
 
-            const participantId = track.getParticipantId();
+            if (FeatureFlags.isSourceNameSignalingEnabled()) {
+                const sourceName = track.getSourceName();
 
-            if (participantId) {
-                const resolution = ssrcStats.resolution;
+                if (sourceName) {
+                    const resolution = ssrcStats.resolution;
 
-                if (resolution.width
-                        && resolution.height
-                        && resolution.width !== -1
-                        && resolution.height !== -1) {
-                    const userResolutions = resolutions[participantId] || {};
+                    if (resolution.width // eslint-disable-line max-depth
+                            && resolution.height
+                            && resolution.width !== -1
+                            && resolution.height !== -1) {
+                        resolutions[sourceName] = resolution;
+                    }
+                    if (ssrcStats.framerate !== 0) { // eslint-disable-line max-depth
+                        framerates[sourceName] = ssrcStats.framerate;
+                    }
+                    if (audioCodec && videoCodec) { // eslint-disable-line max-depth
+                        const codecDesc = {
+                            'audio': audioCodec,
+                            'video': videoCodec
+                        };
 
-                    userResolutions[ssrc] = resolution;
-                    resolutions[participantId] = userResolutions;
+                        codecs[sourceName] = codecDesc;
+                    }
+                } else {
+                    logger.error(`No source name returned by ${track}`);
                 }
-                if (ssrcStats.framerate !== 0) {
-                    const userFramerates = framerates[participantId] || {};
+            } else {
+                const participantId = track.getParticipantId();
 
-                    userFramerates[ssrc] = ssrcStats.framerate;
-                    framerates[participantId] = userFramerates;
-                }
-                if (audioCodec && videoCodec) {
-                    const codecDesc = {
-                        'audio': audioCodec,
-                        'video': videoCodec
-                    };
+                if (participantId) {
+                    const resolution = ssrcStats.resolution;
 
-                    const userCodecs = codecs[participantId] || {};
+                    if (resolution.width // eslint-disable-line max-depth
+                            && resolution.height
+                            && resolution.width !== -1
+                            && resolution.height !== -1) {
+                        const userResolutions = resolutions[participantId] || {};
 
-                    userCodecs[ssrc] = codecDesc;
-                    codecs[participantId] = userCodecs;
+                        userResolutions[ssrc] = resolution;
+                        resolutions[participantId] = userResolutions;
+                    }
+                    if (ssrcStats.framerate !== 0) { // eslint-disable-line max-depth
+                        const userFramerates = framerates[participantId] || {};
+
+                        userFramerates[ssrc] = ssrcStats.framerate;
+                        framerates[participantId] = userFramerates;
+                    }
+                    if (audioCodec && videoCodec) { // eslint-disable-line max-depth
+                        const codecDesc = {
+                            'audio': audioCodec,
+                            'video': videoCodec
+                        };
+
+                        const userCodecs = codecs[participantId] || {};
+
+                        userCodecs[ssrc] = codecDesc;
+                        codecs[participantId] = userCodecs;
+                    }
+                } else {
+                    logger.error(`No participant ID returned by ${track}`);
                 }
-            } else {
-                logger.error(`No participant ID returned by ${track}`);
             }
         }