chrome/test/data/panels/test_extension/manifest.json

{
  "name": "test extension",
  "version": "0.1",
  "manifest_version": 2,
  "description": "Test extension that is used to test panel icon support.",
  "background": {
    "page": "test.html"
  },
  "icons": {
    "128": "128.png",
    "32": "32.png",
    "24": "24.png"
  },
  "permissions": ["tabs"]
}