Examine source code of Page Integrity

{
  "manifest_version": 2,
  "name": "Page Integrity",
  "description": "Extension",
  "version": "1.0.0",
  "permissions": [
    "activeTab",
    "tabs",
    "webRequest",
    "<all_urls>",
    "webRequestBlocking",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "browser_style": true,
    "default_title": "Page Integrity",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/pi-white-16x16.png",
      "32": "icons/pi-white-32x32.png"
    }
  }
}