fix(video-label): Listen to resize events on video elements when possible

modules/UI/videolayout/LargeVideoManager.js

             e => this.onHoverOut(e)
         );
 
-        // TODO Use the onresize event when temasys video objects support it.
-        /**
-         * The interval for checking if the displayed video resolution is or is
-         * not high-definition.
-         *
-         * @private
-         * @type {timeoutId}
-         */
-        this._updateVideoResolutionInterval = window.setInterval(
-            () => this._updateVideoResolutionStatus(),
-            VIDEO_RESOLUTION_POLL_INTERVAL);
+        // Bind event handler so it is only bound once for every instance.
+        this._updateVideoResolutionStatus
+            = this._updateVideoResolutionStatus.bind(this);
+
+        this.videoContainer.addResizeListener(
+            this._updateVideoResolutionStatus);
+
+        if (!JitsiMeetJS.util.RTCUIHelper.isResizeEventSupported()) {
+            /**
+             * An interval for polling if the displayed video resolution is or
+             * is not high-definition. For browsers that do not support video
+             * resize events, polling is the fallback.
+             *
+             * @private
+             * @type {timeoutId}
+             */
+            this._updateVideoResolutionInterval = window.setInterval(
+                this._updateVideoResolutionStatus,
+                VIDEO_RESOLUTION_POLL_INTERVAL);
+        }
     }
 
     /**
-     * Stops any polling intervals on the instance.
+     * Stops any polling intervals on the instance and and removes any
+     * listeners registered on child components.
      *
      * @returns {void}
      */
     destroy() {
         window.clearInterval(this._updateVideoResolutionInterval);
+        this.videoContainer.removeResizeListener(
+            this._updateVideoResolutionStatus);
     }
 
     onHoverIn (e) {

modules/UI/videolayout/VideoContainer.js

         // copied between new <object> elements
         //this.$video.on('play', onPlay);
         this.$video[0].onplay = onPlayCallback;
+
+        /**
+         * A Set of functions to invoke when the video element resizes.
+         *
+         * @private
+         */
+        this._resizeListeners = new Set();
+
+        // As of May 16, 2017, temasys does not support resize events.
+        this.$video[0].onresize = this._onResize.bind(this);
+    }
+
+    /**
+     * Adds a function to the known subscribers of video element resize
+     * events.
+     *
+     * @param {Function} callback - The subscriber to notify when the video
+     * element resizes.
+     * @returns {void}
+     */
+    addResizeListener(callback) {
+        this._resizeListeners.add(callback);
     }
 
     /**
         });
     }
 
+    /**
+     * Removes a function from the known subscribers of video element resize
+     * events.
+     *
+     * @param {Function} callback - The callback to remove from known
+     * subscribers of video resize events.
+     * @returns {void}
+     */
+    removeResizeListener(callback) {
+        this._resizeListeners.delete(callback);
+    }
+
     /**
      * Update video stream.
      * @param {JitsiTrack?} stream new stream
             (this.videoType === VIDEO_CONTAINER_TYPE && !isAvatar)
                 ? "#000" : interfaceConfig.DEFAULT_BACKGROUND);
     }
+
+    /**
+     * Callback invoked when the video element changes dimensions.
+     *
+     * @private
+     * @returns {void}
+     */
+    _onResize() {
+        this._resizeListeners.forEach(callback => callback());
+    }
 }