chrome-extensions-samples/samples/webview-samples/shared-script/manifest.json

{
  "manifest_version": 2,
  "name": "Shared Script Sample: More Dragons!",
  "minimum_chrome_version": "24.0.1307.0",
  "version": "2.0",
  "icons": {
    "16": "icon_16.png",
    "128": "icon_128.png"
  },
  "app": {
    "background": {
      "scripts": ["main.js"]
    }
  },
  "permissions": [
    "webview"
  ]
}