Examine source code of Notifications for Spotify

{
  "name": "Notifications for Spotify",
  "version": "0.4.0",
  "manifest_version": 2,
  "minimum_chrome_version": "49",
  "description": "Add notifications and controls to open.spotify.com",
  "homepage_url": "https://github.com/Skylark95/spotify-notifications",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "src/inject/spotify-notifications.js"
      ],
      "run_at": "document_end"
    }
  ],
  "background": {
    "scripts": [
      "src/bg/background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_icon": "icons/icon19.png",
    "default_title": "Notifications for Spotify",
    "default_popup": "src/browser-action/browser-action.html"
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Alt+Shift+S"
      }
    },
    "spotify-notifications-play-pause": {
      "suggested_key": {
        "default": "Ctrl+Shift+Z"
      },
      "description": "Toggle Play/Pause track"
    },
    "spotify-notifications-show-notification": {
      "suggested_key": {
        "default": "Ctrl+Shift+X"
      },
      "description": "Show Notification"
    }
  },
  "applications": {
    "gecko": {
      "id": "{d3c9958d-fd04-454b-9151-49a2bdb9af63}"
    }
  }
}