@Override
    public HandlerRegistration addValueChangeHandler(final ValueChangeHandler<String> handler) {
        addChangeHandler = true;
        updateChangeHandler();
        return addHandler(handler, ValueChangeEvent.getType());
    }
@param lineNo One based
@param colNo  One based
stroom-core-client-widget/src/main/java/stroom/editor/client/view/Editor.java