fix(media) Deprecate startScreenSharing config option for web browsers.

This is no longer supported as per the w3c spec for getDisplayMedia.

conference.js

@@ -486,7 +486,7 @@ export default {
 
         // Always get a handle on the audio input device so that we have statistics (such as "No audio input" or
         // "Are you trying to speak?" ) even if the user joins the conference muted.
-        const initialDevices = config.disableInitialGUM ? [] : [ 'audio' ];
+        const initialDevices = config.disableInitialGUM ? [] : [ MEDIA_TYPE.AUDIO ];
         const requestedAudio = !config.disableInitialGUM;
         let requestedVideo = false;
 
@@ -494,7 +494,7 @@ export default {
                 && !options.startWithVideoMuted
                 && !options.startAudioOnly
                 && !options.startScreenSharing) {
-            initialDevices.push('video');
+            initialDevices.push(MEDIA_TYPE.VIDEO);
             requestedVideo = true;
         }
 
@@ -518,21 +518,35 @@ export default {
         // spend much time displaying the overlay screen. If GUM is not resolved within 15 seconds it will
         // probably never resolve.
         const timeout = browser.isElectron() ? 15000 : 60000;
+        const audioOptions = {
+            devices: [ MEDIA_TYPE.AUDIO ],
+            timeout,
+            firePermissionPromptIsShownEvent: true,
+            fireSlowPromiseEvent: true
+        };
 
         // FIXME is there any simpler way to rewrite this spaghetti below ?
         if (options.startScreenSharing) {
-            tryCreateLocalTracks = this._createDesktopTrack()
+            // This option has been deprecated since it is no longer supported as per the w3c spec.
+            // https://w3c.github.io/mediacapture-screen-share/#dom-mediadevices-getdisplaymedia. If the user has not
+            // interacted with the webpage before the getDisplayMedia call, the promise will be rejected by the
+            // browser. This has already been implemented in Firefox and Safari and will be implemented in Chrome soon.
+            // https://bugs.chromium.org/p/chromium/issues/detail?id=1198918
+            // Please note that Spot uses the same config option to use an external video input device label as
+            // screenshare and calls getUserMedia instead of getDisplayMedia for capturing the media. Therefore it
+            // needs to be supported here if _desktopSharingSourceDevice is provided.
+            const errMessage = new Error('startScreenSharing config option is no longer supported for web browsers');
+            const desktopPromise = config._desktopSharingSourceDevice
+                ? this._createDesktopTrack()
+                : Promise.reject(errMessage);
+
+            tryCreateLocalTracks = desktopPromise
                 .then(([ desktopStream ]) => {
                     if (!requestedAudio) {
                         return [ desktopStream ];
                     }
 
-                    return createLocalTracksF({
-                        devices: [ 'audio' ],
-                        timeout,
-                        firePermissionPromptIsShownEvent: true,
-                        fireSlowPromiseEvent: true
-                    })
+                    return createLocalTracksF(audioOptions)
                         .then(([ audioStream ]) =>
                             [ desktopStream, audioStream ])
                         .catch(error => {
@@ -545,14 +559,7 @@ export default {
                     logger.error('Failed to obtain desktop stream', error);
                     errors.screenSharingError = error;
 
-                    return requestedAudio
-                        ? createLocalTracksF({
-                            devices: [ 'audio' ],
-                            timeout,
-                            firePermissionPromptIsShownEvent: true,
-                            fireSlowPromiseEvent: true
-                        })
-                        : [];
+                    return requestedAudio ? createLocalTracksF(audioOptions) : [];
                 })
                 .catch(error => {
                     errors.audioOnlyError = error;
@@ -587,13 +594,7 @@ export default {
                             return [];
                         }
 
-                        return (
-                            createLocalTracksF({
-                                devices: [ 'audio' ],
-                                timeout,
-                                firePermissionPromptIsShownEvent: true,
-                                fireSlowPromiseEvent: true
-                            }));
+                        return createLocalTracksF(audioOptions);
                     } else if (requestedAudio && !requestedVideo) {
                         errors.audioOnlyError = err;
 
@@ -615,7 +616,7 @@ export default {
                     // Try video only...
                     return requestedVideo
                         ? createLocalTracksF({
-                            devices: [ 'video' ],
+                            devices: [ MEDIA_TYPE.VIDEO ],
                             firePermissionPromptIsShownEvent: true,
                             fireSlowPromiseEvent: true
                         })

config.js

@@ -236,7 +236,11 @@ var config = {
     //     max: 5
     // },
 
-    // Try to start calls with screen-sharing instead of camera video.
+    // This option has been deprecated since it is no longer supported as per the w3c spec.
+    // https://w3c.github.io/mediacapture-screen-share/#dom-mediadevices-getdisplaymedia. If the user has not
+    // interacted with the webpage before the getDisplayMedia call, the promise will be rejected by the browser. This
+    // has already been implemented in Firefox and Safari and will be implemented in Chrome soon.
+    // https://bugs.chromium.org/p/chromium/issues/detail?id=1198918
     // startScreenSharing: false,
 
     // Recording