Custom ToolBar Component / Resize Logic Problem

I am developing a ToolBar having the drag&drop metaphor to organize the tools (using gwt-dnd library). But i have a doubt. I need to collapse the tools in the toolbar if the width is not enough, as it does in the vaadin menuBar.

The solution provided by GWT to add resize logic in your composite widget is to extend ResizeComposite and implement RequiresResize Interface for the children. But Only it works if the entrypoint is using the RootLayoutPanel object, and i am not sure that vaadin entrypoint uses it.

So i was watching the VMenubar code to find out how vaadin resolves the resize/collapse problem. Using a custom interface, ContainerResizedListener.

Is that interface the unique way to resolve the problem or the GWT solution is also supported?