chrome/test/data/devtools/extensions/devtools_messaging/manifest.json

{
   "description": "Devtools Test extension - messaging",
   "name": "Devtools Test extension - messaging",
   "version": "0.1",
   "manifest_version": 2,
   "devtools_page": "devtools.html",
   "background":  {
       "scripts": [ "background.js" ]
   }
}