google-map-marker shows empty popup window if there are comments in the insertion point

[M. Piao]

The problem is in google-map-marker's _contentChanged method. It should check for existence of non-comment child node instead of a string check.

Example

 <google-map>
    <google-map-marker latitude=30 longitude=30>
        <!-- This is just come comment -->
    </google-map-marker>
</google-map>

[Eric Bidelman]

Want to submit a PR?