title: Edge doesn't stretch iframe in a flexbox
body: <p>The <code>iframe</code> in the following demo is a flex item:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>* {
    margin: 0;
    border: 0;
    padding: 0;
  }
  html,
  body {
    height: 100%;
  }
  body {
    display: flex;
  }
  iframe {
    background: olive;
    flex: 1;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;iframe&gt;&lt;/iframe&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>But it doesn't cover the flex container:</p>
  
  <p><a href="https://i.stack.imgur.com/IdLpU.png" rel="noreferrer"><img src="https://i.stack.imgur.com/IdLpU.png" alt="enter image description here"></a>  </p>
  
  <p>If you replace <code>iframe</code> with a <code>div</code>, it works with no problem.  </p>
  
  <ol>
  <li>Why is that?</li>
  <li>What's the right approach to resolve the issue?</li>
  </ol>