Make window.postMessage grab settings objects before going async

Fixes #894.

source

@@ -92771,6 +92771,9 @@ function receiver(e) {
    <li><p>Let <var>targetRealm</var> be this <code>Window</code> object's <span
    data-x="concept-global-object-realm">Realm</span>.</p></li>
 
+   <li><p>Let <var>entrySettings</var> be the <span>entry settings object</span>.</p></li>
+
+   <li><p>Let <var>incumbentSettings</var> be the <span>incumbent settings object</span>.</p></li>
 
    <li><p>Let <var>cloneRecord</var> be <span>StructuredCloneWithTransfer</span>(<var>message</var>,
    <var>transfer</var>, <var>targetRealm</var>). Rethrow any exceptions.</p></li>
@@ -92789,8 +92792,7 @@ function receiver(e) {
     <p>If the <var>targetOrigin</var> argument is a single literal U+002F SOLIDUS
     character (/), and the <code>Document</code> of the <code>Window</code> object on which the
     method was invoked does not have the <span>same origin</span> as the <span>responsible
-    document</span> specified by the <span>entry settings object</span>, then abort these steps
-    silently.</p>
+    document</span> specified by <var>entrySettings</var>, then abort these steps silently.</p>
 
     <p>Otherwise, if the <var>targetOrigin</var> argument is an <span>absolute URL</span>,
     and the <code>Document</code> of the <code>Window</code> object on which the method was invoked
@@ -92809,11 +92811,11 @@ function receiver(e) {
    initialised to the value of <var>message clone</var>, the <code
    data-x="dom-MessageEvent-origin">origin</code> attribute must be initialised to the <span
    data-x="Unicode serialisation of an origin">Unicode serialisation</span> of the
-   <span>origin</span> specified by the <span>incumbent settings object</span>, the <code
+   <span>origin</span> specified by <var>incumbentSettings</var>, the <code
    data-x="dom-MessageEvent-source">source</code> attribute must be initialised to the
    <code>WindowProxy</code> object corresponding to the <span
    data-x="concept-settings-object-global">global object</span> (a <code>Window</code> object)
-   specified by the <span>incumbent settings object</span>, and the <code
+   specified by <var>incumbentSettings</var>, and the <code
    data-x="dom-MessageEvent-ports">ports</code> attribute must be initialised to the <var>new
    ports</var> array.</p></li> <!-- invariant: the global object is always a Window if the script
    can see this method -->