I've added a section in our style guide on spaces and type annotations. 
https://docs.google.com/a/google.com/document/d/1ZV70oTNWO00bs0RcMwqr3FvKJXA6smYQ2kZ8Zr8YZnw/edit#heading=h.gmob2htqhzm4

I think this can all fit on one line.