function handleFileNew() {
        //var defaultExtension = PreferencesManager.get("defaultExtension");
        //if (defaultExtension) {
        //    defaultExtension = "." + defaultExtension;
        //}
        var defaultExtension = "";  // disable preference setting for now

        var doc = DocumentManager.createUntitledDocument(_nextUntitledIndexToUse++, defaultExtension);
        MainViewManager._edit(MainViewManager.ACTIVE_PANE, doc);

        HealthLogger.sendAnalyticsData(
            HealthLogger.commonStrings.USAGE +
            HealthLogger.commonStrings.FILE_OPEN +
            HealthLogger.commonStrings.FILE_NEW,
            HealthLogger.commonStrings.USAGE,
            HealthLogger.commonStrings.FILE_OPEN,
            HealthLogger.commonStrings.FILE_NEW
        );

        return new $.Deferred().resolve(doc).promise();
    }
Create a new untitled document in the workingset, and make it the current document.
Promise is resolved (synchronously) with the newly-created Document.