Clone <iframe srcdoc>'s node document's CSP list

See w3c/webappsec-csp#207 for context.

Tests: web-platform-tests/wpt#8520.

Fixes #2594.

Author: annevk

source

@@ -2549,8 +2549,9 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
              <dfn data-x="list empty" data-x-href="https://infra.spec.whatwg.org/#list-empty">empty</dfn>,
              <dfn data-x="list contains" data-x-href="https://infra.spec.whatwg.org/#list-contain">contains</dfn>,
              <dfn data-x="list size" data-x-href="https://infra.spec.whatwg.org/#list-size">size</dfn>,
-             <dfn data-x="list is empty" data-x-href="https://infra.spec.whatwg.org/#list-is-empty">is empty</dfn>, and
-             <dfn data-x="list iterate" data-x-href="https://infra.spec.whatwg.org/#list-iterate">iterate</dfn></li>
+             <dfn data-x="list is empty" data-x-href="https://infra.spec.whatwg.org/#list-is-empty">is empty</dfn>,
+             <dfn data-x="list iterate" data-x-href="https://infra.spec.whatwg.org/#list-iterate">iterate</dfn>, and
+             <dfn data-x="list clone" data-x-href="https://infra.spec.whatwg.org/#list-clone">clone</dfn></li>
      <li>The <dfn data-x-href="https://infra.spec.whatwg.org/#stack">stack</dfn> data structure and the associated definitions for
              <dfn data-x="stack push" data-x-href="https://infra.spec.whatwg.org/#stack-push">push</dfn> and
              <dfn data-x="stack pop" data-x-href="https://infra.spec.whatwg.org/#stack-pop">pop</dfn></li>
@@ -29697,9 +29698,10 @@ interface <dfn>HTMLIFrameElement</dfn> : <span>HTMLElement</span> {
     data-x="concept-response-header-list">header list</span> consists of `<code
     data-x="">Content-Type</code>`/`<code>text/html</code>, <span
     data-x="concept-response-body">body</span> is the value of the attribute, <span
-    data-x="concept-response-csp-list">CSP list</span> is the <span
-    data-x="concept-document-csp-list">CSP list</span> of the <code>iframe</code> element's <span>node
-    document</span>, <span data-x="concept-response-https-state">HTTPS state</span> is the <span
+    data-x="concept-response-csp-list">CSP list</span> is a <span data-x="list clone">clone</span>
+    of the <code>iframe</code> element's <span>node document</span>'s <span
+    data-x="concept-document-csp-list">CSP list</span>, <span
+    data-x="concept-response-https-state">HTTPS state</span> is the <span
     data-x="concept-document-https-state">HTTPS state</span> of the <code>iframe</code> element's
     <span>node document</span>.