Don't add custom search engines

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "author": "Greg Sadetsky et al.",
  "manifest_version": 2,
  "name": "Don't add custom search engines",
  "version": "0.0.6",
  "description": "Prevent Google Chrome from auto-adding custom search engines",
  "homepage_url": "https://github.com/gregsadetsky/chrome-dont-add-custom-search-engines",
  "minimum_chrome_version": "49.0.0.0",
  "offline_enabled": true,
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "background": {
    "scripts": [
      "bg.js"
    ]
  },
  "icons": {
    "64": "icon-64.png",
    "128": "icon-128.png"
  },
  "browser_action": {
    "default_title": "Don't add custom search engines",
    "default_icon": "icon-64.png"
  },
  "permissions": [
    "http://*/*",
    "https://*/*"
  ]
}