title: How to set <iframe src="..."> without causing `unsafe value` exception?
body: <p>I am working on a tutorial involving the setting of an <code>iframe</code> <code>src</code> attribute: </p>
  
  <pre><code>&lt;iframe width="100%" height="300" src="{{video.url}}"&gt;&lt;/iframe&gt;
  </code></pre>
  
  <p>This throws an exception:</p>
  
  <pre><code>Error: unsafe value used in a resource URL context
  at DomSanitizationServiceImpl.sanitize...
  </code></pre>
  
  <p>I have already tried using bindings with <code>[src]</code> with no success.</p>