A base layer using OSM tiles.

Tiles graciously provided by OSM (tile.openstreetmap.org)

To use this layer, you must provide attribution to OSM. See:
http://wiki.openstreetmap.org/wiki/Tile_usage_policy
http://wiki.openstreetmap.org/wiki/Legal_FAQ#I_would_like_to_use_OpenStreetMap_maps._How_should_I_credit_you.3F

Usage:
map.mapTypes.set('osm', new OSMBase());

You can do this by creating a new OSMBase.Attribution like this:
new OSMBase.Attribution(map)
The attribution will be shown in the bottom right of the map when the OSM layer is activated.