public ValueBoxEditor<T> asEditor() {
        if (editor == null) {
            editor = ValueBoxEditor.of(this);
        }
        return editor;
    }
Returns an Editor that is backed by the ValueBoxBase. The default
implementation returns {@link ValueBoxEditor#of(ValueBoxBase)}. Subclasses
may override this method to provide custom error-handling when using the
Editor framework.
stroom-core-client-widget/src/main/java/com/google/gwt/user/client/ui/ValueBoxBase.java