The reason these two divs were here and not directly in `<spark-polymer-ui>` was that the respective code had trouble using them that way. With that, the menu and everything else possible should have stayed in `<spark-polymer-ui>`. It should be pretty easy to combine these light DOM elements from here with shadow DOM elements like the menu using `<content select="...">` construct.

But it's ok, you can land this, and I'll rework it later during one of the upcoming iterations on the model/UI architecture.