{
  "manifest_version": 2,
  "name": "Echo",
  "description": "Echo..... Echo.",
  "version": "1",
  "minimum_chrome_version": "23",
  "app": {
    "background": {
      "scripts": ["main.js"]
    }
  },
  "icons": {
    "16": "icon_16.png",
    "128": "icon_128.png"
  },
  "permissions": [
    "experimental",
    "socket"
  ]
}

{
  "manifest_version": 2,
  "name": "Echo",
  "description": "Echo..... Echo.",
  "version": "1",
  "minimum_chrome_version": "23",
  "app": {
    "background": {
      "scripts": ["main.js"]
    }
  },
  "icons": {
    "16": "icon_16.png",
    "128": "icon_128.png"
  },
  "permissions": [
    "experimental",
    {"socket": [
      "udp-send-to"
    ]}
  ]
}

Update socket permission in udp demo
Update socket permission in udp demo