Implement external API notification about screen sharing status

modules/API/API.js

@@ -471,6 +471,20 @@ class API {
         this._sendEvent({ name: 'feedback-submitted' });
     }
 
+    /**
+     * Notify external application (if API is enabled) that the screen sharing
+     * has been turned on/off.
+     *
+     * @param {boolean} on - True if screen sharing is enabled.
+     * @returns {void}
+     */
+    notifyScreenSharingStatusChanged(on: boolean) {
+        this._sendEvent({
+            name: 'screen-sharing-status-changed',
+            on
+        });
+    }
+
     /**
      * Disposes the allocated resources.
      *

modules/API/external/external_api.js

@@ -48,7 +48,8 @@ const events = {
     'video-conference-joined': 'videoConferenceJoined',
     'video-conference-left': 'videoConferenceLeft',
     'video-availability-changed': 'videoAvailabilityChanged',
-    'video-mute-status-changed': 'videoMuteStatusChanged'
+    'video-mute-status-changed': 'videoMuteStatusChanged',
+    'screen-sharing-status-changed': 'screenSharingStatusChanged'
 };
 
 /**
@@ -485,6 +486,12 @@ export default class JitsiMeetExternalAPI extends EventEmitter {
      * {{
      * roomName: room //the room name of the conference
      * }}
+     * screenSharingStatusChanged - receives event notifications about
+     * turning on/off the local user screen sharing.
+     * The listener will receive object with the following structure:
+     * {{
+     * on: on //whether screen sharing is on
+     * }}
      * readyToClose - all hangup operations are completed and Jitsi Meet is
      * ready to be disposed.
      * @returns {void}