Adds setting subject and adding event on receiving such change.

conference.js

     onStartMutedPolicyChanged,
     p2pStatusChanged,
     sendLocalParticipant,
-    setDesktopSharingEnabled
+    setDesktopSharingEnabled,
+    setSubject
 } from './react/features/base/conference';
 import {
     getAvailableDevices,
         room.on(JitsiConferenceEvents.TALK_WHILE_MUTED, () => {
             APP.UI.showToolbar(6000);
         });
+        room.on(JitsiConferenceEvents.SUBJECT_CHANGED,
+            subject => APP.API.notifySubjectChanged(subject));
 
         room.on(
             JitsiConferenceEvents.LAST_N_ENDPOINTS_CHANGED,
         APP.API.notifyAudioMutedStatusChanged(muted);
     },
 
+    /**
+     * Changes the subject of the conference.
+     * Note: available only for moderator.
+     *
+     * @param subject {string} the new subject for the conference.
+     */
+    setSubject(subject) {
+        APP.store.dispatch(setSubject(subject));
+    },
+
     /**
      * Dispatches the passed in feedback for submission. The submitted score
      * should be a number inclusively between 1 through 5, or -1 for no score.

doc/api.md

 api.executeCommand('displayName', 'New Nickname');
 ```
 
+* **subject** - Sets the subject of the conference. This command requires one argument - the new subject to be set.
+```javascript
+api.executeCommand('subject', 'New Conference Subject');
+```
+
 * **toggleAudio** - Mutes / unmutes the audio for the local participant. No arguments are required.
 ```javascript
 api.executeCommand('toggleAudio')
 
 * **readyToClose** - event notification fired when Jitsi Meet is ready to be closed (hangup operations are completed).
 
+* **subjectChange** - event notifications about subject of conference changes. 
+The listener will receive an object with the following structure:
+```javascript
+{
+"subject": subject // the new subject
+}
+```
+
 You can also add multiple event listeners by using `addEventListeners`.
 This method requires one argument of type Object. The object argument must
 have the names of the events as keys and the listeners of the events as values.

modules/API/API.js

         'proxy-connection-event': event => {
             APP.conference.onProxyConnectionEvent(event);
         },
+        'subject': subject => {
+            sendAnalytics(createApiEvent('subject.changed'));
+            APP.conference.setSubject(subject);
+        },
         'submit-feedback': feedback => {
             sendAnalytics(createApiEvent('submit.feedback'));
             APP.conference.submitFeedback(feedback.score, feedback.message);
         });
     }
 
+    /**
+     * Notify external application (if API is enabled) that the conference
+     * changed their subject.
+     *
+     * @param {string} subject - Conference subject.
+     * @returns {void}
+     */
+    notifySubjectChanged(subject: string) {
+        this._sendEvent({
+            name: 'subject-change',
+            subject
+        });
+    }
+
     /**
      * Disposes the allocated resources.
      *

modules/API/external/external_api.js

     displayName: 'display-name',
     email: 'email',
     hangup: 'video-hangup',
+    subject: 'subject',
     submitFeedback: 'submit-feedback',
     toggleAudio: 'toggle-audio',
     toggleChat: 'toggle-chat',
     'video-conference-left': 'videoConferenceLeft',
     'video-availability-changed': 'videoAvailabilityChanged',
     'video-mute-status-changed': 'videoMuteStatusChanged',
-    'screen-sharing-status-changed': 'screenSharingStatusChanged'
+    'screen-sharing-status-changed': 'screenSharingStatusChanged',
+    'subject-change': 'subjectChange'
 };
 
 /**
      * Executes command. The available commands are:
      * {@code displayName} - Sets the display name of the local participant to
      * the value passed in the arguments array.
+     * {@code subject} - Sets the subject of the conference, the value passed
+     * in the arguments array. Note: available only for moderator.
+     *
      * {@code toggleAudio} - Mutes / unmutes audio with no arguments.
      * {@code toggleVideo} - Mutes / unmutes video with no arguments.
      * {@code toggleFilmStrip} - Hides / shows the filmstrip with no arguments.

react/features/base/conference/actionTypes.js

  */
 export const SET_AUDIO_ONLY = Symbol('SET_AUDIO_ONLY');
 
+/**
+ * The type of (redux) action, which indicates to set conference subject.
+ *
+ * {
+ *     type: SET_CONFERENCE_SUBJECT
+ *     subject: string
+ * }
+ */
+export const SET_CONFERENCE_SUBJECT = Symbol('SET_CONFERENCE_SUBJECT');
+
 /**
  * The type of (redux) action which sets the desktop sharing enabled flag for
  * the current conference.

react/features/base/conference/actions.js

     LOCK_STATE_CHANGED,
     P2P_STATUS_CHANGED,
     SET_AUDIO_ONLY,
+    SET_CONFERENCE_SUBJECT,
     SET_DESKTOP_SHARING_ENABLED,
     SET_FOLLOW_ME,
     SET_LASTN,
         return dispatch(setAudioOnly(!audioOnly, true));
     };
 }
+
+/**
+ * Changing conference subject.
+ *
+ * @param {string} subject - The new subject.
+ * @returns {void}
+ */
+export function setSubject(subject: String) {
+    return {
+        type: SET_CONFERENCE_SUBJECT,
+        subject
+    };
+}

react/features/base/conference/middleware.js

     CONFERENCE_WILL_LEAVE,
     DATA_CHANNEL_OPENED,
     SET_AUDIO_ONLY,
+    SET_CONFERENCE_SUBJECT,
     SET_LASTN,
     SET_ROOM
 } from './actionTypes';
     case SET_AUDIO_ONLY:
         return _setAudioOnly(store, next, action);
 
+    case SET_CONFERENCE_SUBJECT:
+        return _setSubject(store, next, action);
+
     case SET_LASTN:
         return _setLastN(store, next, action);
 
 
     return result;
 }
+
+/**
+ * Changing conference subject.
+ *
+ * @param {Store} store - The redux store in which the specified {@code action}
+ * is being dispatched.
+ * @param {Dispatch} next - The redux {@code dispatch} function to dispatch the
+ * specified {@code action} to the specified {@code store}.
+ * @param {Action} action - The redux action which is being dispatched in the
+ * specified {@code store}.
+ * @private
+ * @returns {Object} The value returned by {@code next(action)}.
+ */
+function _setSubject({ getState }, next, action) {
+    const { conference } = getState()['features/base/conference'];
+    const { subject } = action;
+
+    if (subject) {
+        conference.setSubject(subject);
+    }
+
+    return next(action);
+}