code: function injectScript (scriptName, cb) {
    const src = `
      (function() {
        var script = document.constructor.prototype.createElement.call(document, 'script');
        script.src = "${scriptName}";
        document.documentElement.appendChild(script);
        script.parentNode.removeChild(script);
      })()
    `
    chrome.devtools.inspectedWindow.eval(src, function (res, err) {
      if (err) {
        console.log(err)
      }
      cb()
    })
  }
docs: Inject a globally evaluated script, in the same context with the actual
  user app.
  
  @param {String} scriptName
  @param {Function} cb