Chrome Extension with background and contentScript entries

manifest.json

{
  "name": "My Extension",
  "version": "1.0.0",
  "description": "Description here",
  "manifest_version": 2,
  "permissions": ["webNavigation", "tabs"],
  "page_action": {
    "default_popup": "index.html"
  },
  "background": {
    "scripts": ["background.js", "runtime.js"]
  },
  "content_scripts": [
    {
      "matches": ["*://*.github.com/*"],
      "js": ["contentScript.js", "runtime.js"]
    }
  ]
}