title: Import external html containing script tag - doesn't work
body: <p>I have an <code>index.html</code></p>
  
  <pre><code>&lt;!doctype html&gt;
  &lt;html lang="en"&gt;
  &lt;head&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;title&gt;MyApp&lt;/title&gt;
    &lt;link rel="import" href="./common.html"&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;app-root&gt;&lt;/app-root&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>and an external HTML file <code>common.html</code> which contains a script tag</p>
  
  <pre><code>&lt;script&gt;
    window.MY_APP = {
      MY_SETTINGS: {}
    }
  &lt;/script&gt;
  </code></pre>
  
  <p>As you can see I am importing <code>common.html</code> in <code>index.html</code>. The problem is that <code>MY_APP</code> becoming undefined after a successful render of index.html. 
  I could see success call to common.html file in the network tab(Testing in Chrome browser - V 80.**).</p>
  
  <p>This used to work seamlessly earlier but now broken.</p>
  
  <p>Did anyone face this problem? or does anyone know what is happening? Thanks in Advance.</p>