Base64 encode/decode selected text

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "name": "Base64 encode/decode selected text",
  "version": "0.2.1",
  "description": "A base64 encoder/decoder extensions for the chrome",
  "default_locale": "en",
  "permissions": [
    "contextMenus",
    "http://*/*",
    "https://*/*"
  ],
  "background": {
    "scripts": [
      "./background.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "./content_scripts.js"
      ]
    }
  ],
  "icons": {
    "16": "./icons/16.png",
    "48": "./icons/48.png",
    "128": "./icons/128.png"
  }
}