private void doDelayedLayout() {
        if (delayedLayoutCommand == null) {
            delayedLayoutCommand = () -> {
                delayedLayoutCommand = null;
                doLayout();
            };
            Scheduler.get().scheduleDeferred(delayedLayoutCommand);
        }
    }
The element that masks the screen so we can catch mouse events over
iframes.
stroom-core-client-widget/src/main/java/com/google/gwt/user/client/ui/ThinSplitLayoutPanel.java