Examine source code of QuickType

{
  "manifest_version": 2,
  "name": "QuickType",
  "version": "1.0",
  "description": "Adds a popup typing game to the toolbar.",
  "icons": {
    "48": "icons/keys48.png",
    "96": "icons/keys96.png"
  },
  "browser_action": {
    "default_icon": "icons/keys32.png",
    "default_title": "QuickType",
    "default_popup": "popup/popup.html"
  }
}