Examine source code of Storage usage show

{
  "name": "Storage usage show",
  "description": "Show how much storage space a website's data is taking in browser",
  "manifest_version": 2,
  "version": "0.5",
  "homepage_url": "https://garywill.github.io",
  "developer": {
    "name": "Garywill"
  },
  "permissions": [
    "*://*/*",
    "<all_urls>",
    "tabs",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject.js"
      ]
    }
  ],
  "icons": {
    "128": "icon.png"
  },
  "background": {
    "page": "background.html"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Storage usage show"
  },
  "options_ui": {
    "page": "options.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{734146e3-7120-4373-9fd4-5be378e3544a}"
    }
  }
}