electron/spec/fixtures/extensions/content-script-document-start/manifest.json

{
    "name": "document-start",
    "version": "1.0",
    "description": "",
    "content_scripts": [
      {
        "matches": ["<all_urls>"],
        "js": ["start.js"],
        "run_at": "document_start"
      }
    ],
    "manifest_version": 2
}