title: Passive mixed-content is blocked as if it was active mixed-content
body: <p>The <a href="https://developer.mozilla.org/en-US/docs/Web/Security/Mixed_content" rel="nofollow noreferrer">Mozilla page about mixed content</a> specifies two types of mixed content: passive and active.</p>
  <blockquote>
  <p>Mixed passive/display content is content served over HTTP that is
  included in an HTTPS webpage, but that cannot alter other portions of
  the webpage.</p>
  <h3>Passive content list</h3>
  <p>This section lists all types of HTTP requests which are considered
  passive content:</p>
  <ul>
  <li>&lt; img &gt; (src attribute)</li>
  <li>&lt; audio &gt; (src attribute)</li>
  <li>&lt; video &gt; (src attribute)</li>
  <li>&lt; object &gt; subresources (when an  performs HTTP requests)</li>
  </ul>
  </blockquote>
  <p>The <a href="https://developers.google.com/web/fundamentals/security/prevent-mixed-content/fixing-mixed-content" rel="nofollow noreferrer">Google developers page</a> uses the same distinction, and specifies the kind of errors Chrome will display for each of those:</p>
  <p><a href="https://i.stack.imgur.com/XPw9Sm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XPw9Sm.png" alt="Passive mixed-content" /></a>
  <em>Passive mixed-content</em></p>
  <p><a href="https://i.stack.imgur.com/dbPFcm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dbPFcm.png" alt="Active mixed-content" /></a>
  <em>Active mixed-content</em></p>
  <p>So the specs are pretty clear: active mixed content (scripts, css, etc.) is blocked and throws a big red error; passive mixed content (images, videos, etc.) is not blocked but throws nice and yellow warnings.</p>
  <p>Then, why do I have this:</p>
  <p><a href="https://i.stack.imgur.com/e1dFO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/e1dFO.png" alt="Blocked passive mixed-content" /></a></p>
  <p>This comes from an &lt; img &gt; tag, and is clearly recognized by Chrome as an image - but it is blocked in the same way as active mixed content, with big red warnings and all.</p>
  <p>How comes?</p>