Make upgrade an element throw more

In particular if folks disable support for ShadowRoot and ElementInternals, this will make upgrade an element throw a NotSupportedError so element constructors only run with expected state.

Tests: web-platform-tests/wpt#17162.

Author: annevk

source

@@ -3149,7 +3149,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-documenttype"><code>DocumentType</code></dfn> interface</li>
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-childnode"><code>ChildNode</code></dfn> interface</li>
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-element"><code>Element</code></dfn> interface</li>
-     <li><dfn data-x="dom-element-attachshadow" data-x-href="https://dom.spec.whatwg.org/#dom-element-attachshadow"><code>attachShadow()</code></dfn> method.</li>
+     <li><dfn data-x="dom-Element-attachShadow" data-x-href="https://dom.spec.whatwg.org/#dom-element-attachshadow"><code>attachShadow()</code></dfn> method.</li>
+     <li>An element's <dfn data-x="concept-element-shadow-root" data-x-href="https://dom.spec.whatwg.org/#concept-element-shadow-root">shadow root</dfn></li>
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-node"><code>Node</code></dfn> interface</li>
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-nodelist"><code>NodeList</code></dfn> interface</li>
      <li><dfn data-x-href="https://dom.spec.whatwg.org/#interface-processinginstruction"><code>ProcessingInstruction</code></dfn> interface</li>
@@ -67039,7 +67040,7 @@ document.body.append(parent);
 
    <dt>A <dfn data-x="concept-custom-element-definition-disable-shadow" data-export=""
    data-dfn-for="custom element definition">disable shadow</dfn> boolean</dt>
-   <dd>Controls <code data-x="dom-element-attachshadow">attachShadow()</code>.
+   <dd>Controls <code data-x="dom-Element-attachShadow">attachShadow()</code>.
   </dl>
 
   <p>To <dfn data-export="">look up a custom element definition</dfn>, given a <var>document</var>,
@@ -67544,6 +67545,19 @@ customElements.define("x-foo", class extends HTMLElement {
     <p>Run the following substeps while catching any exceptions:</p>
 
     <ol>
+     <li>
+      <p>If <var>definition</var>'s <span
+      data-x="concept-custom-element-definition-disable-shadow">disable shadow</span> is true and
+      <var>element</var>'s <span data-x="concept-element-shadow-root">shadow root</span> is
+      non-null, then throw a <span>"<code>NotSupportedError</code>"</span>
+      <code>DOMException</code>.</p>
+
+      <p class="note">This is needed as <code
+      data-x="dom-Element-attachShadow">attachShadow()</code> does not use <span>look up a custom
+      element definition</span> while <code data-x="dom-attachInternals">attachInternals()</code>
+      does.</p>
+     </li>
+
      <li>
       <p>Let <var>constructResult</var> be the result of <span
       data-x="es-constructing-callback-functions">constructing</span> <var>C</var>, with no