Use img referrerpolicy attribute when fetching images

When initiating a fetch as part of the two image-fetching algorithms
(see #1643), we should use the element's referrerpolicy attribute to set
the referrer policy on the request.

See #1531 and
w3c/webappsec-referrer-policy#40.

Author: estark37

source

@@ -25524,6 +25524,9 @@ interface <dfn>HTMLImageElement</dfn> : <span>HTMLElement</span> {
 
     <p>&#x231B; Set <var>request</var>'s <span>same-origin data-URL flag</span>.</p>
 
+    <p>&#x231B; Set <var>request</var>'s <span>referrer policy</span> to the current state of the
+    element's <code data-x="attr-img-referrerpolicy">referrerpolicy</code> attribute.</p>
+
     <!--FETCH--><p>&#x231B; <span data-x="concept-fetch">Fetch</span> <var>request</var>. Let this
     instance of the <span data-x="concept-fetch">fetching</span> algorithm be associated with
     <var>image request</var>.<!-- TODO "Interaction with the Preload Scanner" from the picture spec
@@ -26416,6 +26419,9 @@ interface <dfn>HTMLImageElement</dfn> : <span>HTMLElement</span> {
      data-x="">imageset</code>", and set <var>request</var>'s <span>synchronous
      flag</span>.</p></li>
 
+     <li><p>Set <var>request</var>'s <span>referrer policy</span> to the current state of the
+     element's <code data-x="attr-img-referrerpolicy">referrerpolicy</code> attribute.</p></li>
+
      <!--FETCH--><li><p>Let <var>response</var> be the result of <span
      data-x="concept-fetch">fetching</span> <var>request</var>.</p></li>
 
@@ -119219,6 +119225,7 @@ INSERT INTERFACES HERE
   Elliott Sprehn,
   Elliotte Harold,
   Emilio Cobos,
+  Emily Stark,
   Eric Carlson,
   Eric Casler,
   Eric Lawrence,