text: Title: How To setting the mobile emulation of userAgent
  Body: mobile_emulation = {
      "deviceMetrics": { "width": 360, "height": 640, "pixelRatio": 3.0 },
      "userAgent": "Mozilla/5.0 (Linux; Android 4.2.1; en-us; Nexus 5 Build/JOP40D) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.166 Mobile Safari/535.19" }
  chrome_options = Options()
  chrome_options.add_experimental_option("mobileEmulation", mobile_emulation)
  
  
  I have tried the capabilities in json format seems not work, could you have any advice? 
  
  Thanks