Dogcheck from Undertale as error pages

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Dogcheck from Undertale as error pages",
  "description": "Replaces all error pages with dogcheck from Undertale",
  "version": "1.0",
  "manifest_version": 2,
  "icons": {
    "128": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "webRequest",
    "<all_urls>"
  ],
  "web_accessible_resources": [
    "dogcheck.html"
  ]
}