Consider extending from google-map

[ebidel]

A lot of its properties are re-implemented for this element.

[robdodson]

@ebidel I think these are the 3 repeated properties: apiKey version sensor. It also has a zoom property but it's zooming the panorama, and disableDefaultUI, which I think the map implements as well?

apiKey version sensor are passed through to the google-maps-api element. Which makes me wonder if both google-map and google-streetview-pano should extend from a more basic element like google-map-base or something. That may be preferable over inheriting from google-map itself since google-map has a lot of properties and methods that have nothing to do with streetview, for instance: latitude longitude showCenterMarker map mapType

[ebidel]

I'm meeting with Maps folks this week. I'll see what they think. There may be more shared in the future that they're aware of, but we're not using yet.