Fixes getDisplayMedia after moving it to nvaigator.mediaDevices.

modules/RTC/ScreenObtainer.js

      * @param errorCallback - The error callback.
      */
     obtainScreenFromGetDisplayMedia(options, callback, errorCallback) {
-        navigator.getDisplayMedia({ video: true })
+        navigator.mediaDevices.getDisplayMedia({ video: true })
             .then(stream => {
                 let applyConstraintsPromise;
 

modules/browser/BrowserCapabilities.js

      * @returns {boolean} {@code true} if the browser supposrts getDisplayMedia.
      */
     supportsGetDisplayMedia() {
-        return navigator.getDisplayMedia !== undefined;
+        return navigator.mediaDevices
+            && navigator.mediaDevices.getDisplayMedia !== undefined;
     }
 
     /**