Use fullscreen logic for initial about:blank documents too

Fixes #1385.

(It seems this was an oversight
8359fee resulting from having two
places to initialize document objects as the result of navigation.
Cleaning that up is a larger separate task.)

source

@@ -80050,30 +80050,47 @@ callback <dfn>FrameRequestCallback</dfn> = void (<span>DOMHighResTimeStamp</span
 
   <hr>
 
-  <p>When a user agent is to <dfn>implement the sandboxing</dfn> for a <code>Document</code>, it
-  must populate <code>Document</code>'s <span>active sandboxing flag set</span> with the union of
-  the flags that are present in the following <span data-x="sandboxing flag set">sandboxing flag
-  sets</span> at the time the <code>Document</code> object is created:</p>
+  <p>To <dfn>implement the sandboxing</dfn> for a <code>Document</code> object <var>document</var>,
+  run these steps:</p>
 
-  <ul>
+  <ol>
+   <li>
+    <p>Populate <var>document</var>'s <span>active sandboxing flag set</span> with the union of the
+    flags that are present in the following <span data-x="sandboxing flag set">sandboxing flag
+    sets</span>:</p>
 
-   <li><p>If the <code>Document</code>'s <span data-x="concept-document-bc">browsing context</span>
-   is a <span>top-level browsing context</span>, then: the flags set on the <span>browsing
-   context</span>'s <span>popup sandboxing flag set</span>.</p></li>
+    <ul>
+     <li><p>If <var>document</var>'s <span data-x="concept-document-bc">browsing context</span> is a
+     <span>top-level browsing context</span>, then: the flags set on the <span>browsing
+     context</span>'s <span>popup sandboxing flag set</span>.</p></li>
 
-   <li><p>If the <code>Document</code>'s <span data-x="concept-document-bc">browsing context</span>
-   is a <span>nested browsing context</span>, then: the flags set on the <span>browsing
-   context</span>'s <span><code>iframe</code> sandboxing flag set</span>.</p></li>
+     <li><p>If <var>document</var>'s <span data-x="concept-document-bc">browsing context</span> is a
+     <span>nested browsing context</span>, then: the flags set on the <span>browsing
+     context</span>'s <span><code>iframe</code> sandboxing flag set</span>.</p></li>
 
-   <li><p>If the <code>Document</code>'s <span data-x="concept-document-bc">browsing context</span>
-   is a <span>nested browsing context</span>, then: the flags set on the <span>browsing
-   context</span>'s <span>parent browsing context</span>'s <span>active document</span>'s
-   <span>active sandboxing flag set</span>.</p></li>
+     <li><p>If <var>document</var>'s <span data-x="concept-document-bc">browsing context</span> is a
+     <span>nested browsing context</span>, then: the flags set on the <span>browsing
+     context</span>'s <span>parent browsing context</span>'s <span>active document</span>'s
+     <span>active sandboxing flag set</span>.</p></li>
 
-   <li><p>The flags set on the <code>Document</code>'s resource's <span>forced sandboxing flag
-   set</span>, if it has one.</p></li>
+     <li><p>The flags set on <var>document</var>'s resource's <span>forced sandboxing flag
+     set</span>, if it has one.</p></li>
+    </ul>
+   </li>
 
-  </ul>
+   <li id="fullscreen-logic"><p>If the <span>active sandboxing flag set</span> of
+   <var>document</var>'s <span data-x="concept-document-bc">browsing context</span> or any of its
+   <span data-x="ancestor browsing context">ancestor browsing contexts</span> (if any) have the
+   <span>sandboxed fullscreen browsing context flag</span> set, then abort these steps.</p></li>
+
+   <li><p>If <var>document</var>'s <span data-x="concept-document-bc">browsing context</span> has a
+   <span>browsing context container</span> and either it is not an <code>iframe</code> element, or
+   it does not have the <code data-x="attr-iframe-allowfullscreen">allowfullscreen</code> attribute
+   specified, or its <span>node document</span> does not have the <span>fullscreen enabled
+   flag</span> set, then also abort these steps.</p></li>
+
+   <li><p>Set <var>document</var>'s <span>fullscreen enabled flag</span>.</p></li>
+  </ol>
 
 
 
@@ -82260,23 +82277,6 @@ State: &lt;OUTPUT NAME=I>1&lt;/OUTPUT> &lt;INPUT VALUE="Increment" TYPE=BUTTON O
      </li>
 
      <li><p><span>Implement the sandboxing</span> for the <code>Document</code>.</p></li>
-
-     <li id="fullscreen-logic">
-
-      <p>If the <span>active sandboxing flag set</span> of the <code>Document</code>'s
-      <span data-x="concept-document-bc">browsing context</span> or any of its <span
-      data-x="ancestor browsing context">ancestor browsing contexts</span> (if any) have the
-      <span>sandboxed fullscreen browsing context flag</span> set, then skip this step.</p>
-
-      <p>If the <code>Document</code>'s <span data-x="concept-document-bc">browsing context</span>
-      has a <span>browsing context container</span> and either it is not an <code>iframe</code>
-      element, or it does not have the <code
-      data-x="attr-iframe-allowfullscreen">allowfullscreen</code> attribute specified, or its
-      <code>Document</code> does not have the <span>fullscreen enabled flag</span> set, then also
-      skip this step.</p>
-
-      <p>Otherwise, set the <code>Document</code>'s <span>fullscreen enabled flag</span>.</p>
-
     </ol>
 
    </li>