GoogleWebComponents/google-map — pull request #40 by davidwittenbrink (2014-08-08 15:14:16+00:00)
Title: Option to have at most one infoWindow open at any time

I needed a way to have at most one infoWindow open at a time and figured other people might too.
If the attribute 'singleInfoWindow' on the 'google-map' element is set to true, it will inform all its children 'google-map-marker' elements to close the other info windows when being clicked.