Adding final step to mask cross-origin

rebase

rebase

Fix modal check in dialog closing algorithm

The value for is modal needs to be cached. This was pointed out here:
whatwg#9178 (comment).

source

@@ -60726,6 +60726,9 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
    <li><p>Let <var>wasModal</var> be the value of <var>subject</var>'s <span>is
    modal</span> flag.</p></li>
 
+   <li><p>Let <var>wasModal</var> be the value of <var>subject</var>'s <span>is
+   modal</span> flag.</p></li>
+
    <li><p>Set the <span>is modal</span> flag of <var>subject</var> to false.</p></li>
 
    <li><p>If <var>result</var> is not null, then set the <code
@@ -100314,6 +100317,69 @@ location.href = '#foo';</code></pre>
   </li>
  </ol>
 
+ <p>To <dfn>build NotRestoredReasons object for page</dfn> given <code>Document state</code>
+ <var>documentState</var>:
+ <ol>
+  <li><p><span>Assert</span>: <var>documentState</var>'s <span
+  data-x="document-state-document">document</span>'s <span>node navigable</span> is a
+  <span>top-level traversable</span>.</p></li>
+
+  <li><p><span>Build NotRestoredReasons object for document</span> given <var>documentState</var>'s
+  <span data-x="document-state-document">document</span>.</p></li>
+
+  <li><p>Count the number of <var>documentState</var>'s <span
+  data-x="document-state-document">document</span>'s <span>descendant navigables</span> whose
+  <span data-x="concept-document-origin">origin</span> is not <span>same origin</span> with
+  <var>documentState</var>'s <span data-x="document-state-document">document</span>.</p>
+
+   <ol>
+    <li><p>Let <var>crossOriginDescendants</var> be an empty <span>list</span>.</p></li>
+
+    <li><p><span data-x="list iterate">For each</span> <var>navigable</var> of
+    <var>documentState</var>'s <span data-x="document-state-document">document</span>'s
+    <span>descendant navigables</span>:</p>
+      <ol>
+       <li><p>If <var>navigable</var>'s <span data-x="nav-document">active document</span>'s
+       <span data-x="concept-document-origin">origin</span> is not <span>same origin</span> with
+       <var>documentState</var>'s <span data-x="document-state-document">document</span>, then <span
+       data-x="list append">append</span> <var>navigable</var> to
+       <var>crossOriginDescendants</var>.</p></li>
+      </ol>
+    </li>
+
+    <li><p>Set <var>crossOriginCount</var> be <var>crossOriginDescendants</var>'s <span
+    data-x="list size">size</span>.</p></li>
+    </ol>
+  </li>
+
+  <li><p>Let <var>randomIndex</var> be a randomly selected integer from 0 to
+  <var>crossOriginCount</var>-1.</p></li>
+
+  <li><p>Let <var>index</var> be 0.</p></li>
+
+  <li><p><span data-x="list iterate">For each</span> <var>crossOriginDescendants</var>:</p>
+   <ol>
+    <li><p>Let <var>reasonsForCrossOriginChild</var> be <var>navigable</var>'s <span
+    data-x="nav-document">active document</span>'s <span>document state</span>'s <span
+    data-x="document-state-not-restored-reasons">notRestoredReasons</span>.</p></li>
+
+    <li><p>Set <var>reasonsForCrossOriginChild</var>'s <span
+    data-x="dom-not-restored-reasons-url">url</span> to null.</p></li>
+
+      <li><p>Set <var>reasonsForCrossOriginChild</var>'s <span
+      data-x="dom-not-restored-reasons-url">url</span> be null.</p></li>
+
+      <li><p>Set <var>reasonsForCrossOriginChild</var>'s <span
+      data-x="dom-not-restored-reasons-reasons">reasons</span> be null.</p></li>
+
+      <li><p>Set <var>reasonsForCrossOriginChild</var>'s <span
+       data-x="dom-not-restored-reasons-children">children</span> be null.</p></li>
+     </ol>
+    </li>
+   </ol>
+  </li>
+ </ol>
+
  <p>To <dfn>build NotRestoredReasons object for page</dfn> given <code>Document state</code>
  <var>documentState</var>:
  <ol>