Prevent Tab Closing

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "name": "Prevent Tab Closing",
  "version": "0.0.2",
  "description": "Prevents tabs from closing unexpectedly. Using dialog 'Are you sure?'",
  "icons": {
    "16": "16x16.png",
    "48": "48x48.png",
    "128": "128x128.png"
  },
  "browser_action": {
    "default_title": "Prevent tab from closing unexpectedly",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_idle",
      "js": [
        "core.js"
      ]
    }
  ],
  "permissions": [
    "storage"
  ],
  "web_accessible_resources": [
    "page.js"
  ]
}