Examine source code of flash-back

{
  "name": "FlashBack",
  "description": "Get back in browser history in a flash",
  "version": "1.0.0",
  "manifest_version": 2,
  "icons": {
    "48": "icons/icon_48.png",
    "128": "icons/icon_128.png"
  },
  "browser_action": {
    "default_title": "FlashBack",
    "default_popup": "popup/popup.html"
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Ctrl+Shift+Y",
        "mac": "Command+Shift+Y"
      },
      "description": "Opens popup"
    }
  },
  "permissions": [
    "history",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'"
}