private void doLayout() {
        if ((hSplits != null || vSplits != null)) {
            // Adjust the split sizes.
            adjustSplitSizes();
        } else {
            super.onResize();
        }
    }
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