Limit crossOrigin reflection to only known values

Matches all browsers: https://jsfiddle.net/7xLu3rLe/1/

wpt already tests this, and matches the behavior the spec is being
changed to:

https://github.com/w3c/web-platform-tests/blob/efb6b0d7/html/dom/elements-metadata.js#L12
https://github.com/w3c/web-platform-tests/blob/efb6b0d7/html/dom/elements-embedded.js#L8
https://github.com/w3c/web-platform-tests/blob/efb6b0d7/html/dom/elements-embedded.js#L90
https://github.com/w3c/web-platform-tests/blob/efb6b0d7/html/dom/elements-embedded.js#L106
https://github.com/w3c/web-platform-tests/blob/efb6b0d7/html/dom/elements-misc.js#L17

Author: ayg

source

@@ -13267,7 +13267,7 @@ interface <dfn>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
 
   <p>The <dfn><code data-x="dom-link-crossOrigin">crossOrigin</code></dfn> IDL attribute must
   <span>reflect</span> the <code data-x="attr-link-crossorigin">crossorigin</code> content
-  attribute.</p>
+  attribute, <span>limited to only known values</span>.</p>
 
   <p>The <dfn><code data-x="dom-link-referrerPolicy">referrerPolicy</code></dfn> IDL attribute must
   <span>reflect</span> the <code data-x="attr-link-referrerpolicy">referrerpolicy</code>
@@ -25621,7 +25621,8 @@ interface <dfn>HTMLImageElement</dfn> : <span>HTMLElement</span> {
   respective content attributes of the same name.</p>
 
   <p>The <dfn data-x="dom-img-crossOrigin"><code>crossOrigin</code></dfn> IDL attribute must
-  <span>reflect</span> the <code data-x="attr-img-crossorigin">crossorigin</code> content attribute.</p>
+  <span>reflect</span> the <code data-x="attr-img-crossorigin">crossorigin</code> content attribute,
+  <span>limited to only known values</span>.</p>
 
   <p>The <dfn data-x="dom-img-useMap"><code>useMap</code></dfn> IDL attribute must
   <span>reflect</span> the <code data-x="attr-hyperlink-usemap">usemap</code> content attribute.</p>
@@ -32233,7 +32234,8 @@ interface <dfn>HTMLMediaElement</dfn> : <span>HTMLElement</span> {
   name.</p>
 
   <p>The <dfn><code data-x="dom-media-crossOrigin">crossOrigin</code></dfn> IDL attribute must
-  <span>reflect</span> the <code data-x="attr-media-crossorigin">crossorigin</code> content attribute.</p>
+  <span>reflect</span> the <code data-x="attr-media-crossorigin">crossorigin</code> content
+  attribute, <span>limited to only known values</span>.</p>
 
   </div>
 
@@ -57508,7 +57510,8 @@ interface <dfn>HTMLScriptElement</dfn> : <span>HTMLElement</span> {
   content attributes of the same name.</p>
 
   <p>The <dfn><code data-x="dom-script-crossOrigin">crossOrigin</code></dfn> IDL attribute must
-  <span>reflect</span> the <code data-x="attr-script-crossorigin">crossorigin</code> content attribute.</p>
+  <span>reflect</span> the <code data-x="attr-script-crossorigin">crossorigin</code> content
+  attribute, <span>limited to only known values</span>.</p>
 
   <p>The <dfn><code data-x="dom-script-noModule">noModule</code></dfn> IDL attribute must
   <span>reflect</span> the <code data-x="attr-script-nomodule">nomodule</code> content