Examine source code of Frontier Slither

{
  "manifest_version": 2,
  "name": "Frontier Slither",
  "description": "Cutting-edge MOD for playing slither.io more comfortably.",
  "version": "1.5",
  "author": "saya",
  "browser_action": {
    "default_popup": "popup.htm",
    "default_title": "Frontier Slither"
  },
  "content_scripts": [
    {
      "js": [
        "inject.js"
      ],
      "matches": [
        "*://slither.io/"
      ],
      "all_frames": false,
      "run_at": "document_end"
    }
  ],
  "content_security_policy": "script-src 'self' https://www.googletagmanager.com; object-src 'self'",
  "permissions": [
    "*://slither.io/",
    "storage"
  ],
  "icons": {
    "128": "icon_128.png"
  },
  "web_accessible_resources": [
    "*.js",
    "*.css"
  ]
}