tern.googleapi provides the gmaps tern plugin which gives you a support for Google Maps JavaScript API.

After installing and converting your project as Tern Project, go at Tern project property, click on Tern / Modules item and select the Google Maps tern plugin and the version :

After that you can benefit with Google Maps completion :

Completion works for Google Maps method :

This Google Maps tern plugin can be used inside WebBrowser. You can see demo here.

Object literal

Completion for object literal :

Validation for object literal (which is available if you enable the (Semantic) Lint linter) :

Web Browser

You can play with online demo which uses CodeMirror (inside Web Browser).