title: How to get content-type from selenium page_source
body: <p>I know the content-type can be gotten from </p>
  
  <pre><code>response = urllib2.urlopen(url)
  content-type = response.info().getheader('Content-type')
  </code></pre>
  
  <p>Now, I need to execute js code so I choose selenium with Phantomjs to fetch web page.</p>
  
  <pre><code>driver = webdriver.PhantomJS()
  driver.get(url)
  source = driver.page_source
  </code></pre>
  
  <p>How can I get content-type from source without downloading web page twice? I know I can save the response.read() as html file, and then driver render the local html file without downloading it again. However, it's too slow. Any suggestions?  </p>