text: /**
   * injectScript - Inject internal script to available access to the `window`
   *
   * @param  {type} file_path Local path of the internal script.
   * @param  {type} tag The tag as string, where the script will be append (default: 'body').
   * @see    {@link http://stackoverflow.com/questions/20499994/access-window-variable-from-content-script}
   */
  function injectScript(file_path, tag) {
      var node = document.getElementsByTagName(tag)[0];
      var script = document.createElement('script');
      script.setAttribute('type', 'text/javascript');
      script.setAttribute('src', file_path);
      node.appendChild(script);
  }
  injectScript(chrome.extension.getURL('content.js'), 'body');
  