Remove the concept of creator Document so we don't leak a document

Fixes #792.

source

@@ -6784,8 +6784,8 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
 
     <p>If <span>the document's address</span> is <code>about:blank</code>, and the
     <code>Document</code>'s <span data-x="concept-document-bc">browsing context</span> has a
-    <span>creator browsing context</span>, then return the <span>document base URL</span> of the
-    <span>creator <code>Document</code></span>, and abort these steps.</p>
+    <span>creator browsing context</span>, then return the <span>creator base URL</span> and abort
+    these steps.</p>
 
    </li>
 
@@ -76081,9 +76081,11 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
   <span>browsing context</span> has no <span>creator browsing context</span>.</p>
 
   <p>If a <span>browsing context</span> <var>A</var> has a <span>creator browsing
-  context</span>, then the <code>Document</code> that was the <span>active document</span> of that
-  <span>creator browsing context</span> at the time <var>A</var> was created is the
-  <dfn>creator <code>Document</code></dfn>.</p>
+  context</span>, then the <dfn>creator origin</dfn>, <dfn>creator URL</dfn>, and <dfn>creator base
+  URL</dfn> are the <span>origin</span>, <span data-x="the document's address">address</span>, and
+  <span data-x="document base URL">base URL</span>, respectively, of the <code>Document</code> that
+  was the <span>active document</span> of that <span>creator browsing context</span> at the time
+  <var>A</var> was created.</p>
 
   <div w-nodev>
 
@@ -76126,19 +76128,18 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
 
     <ul>
      <li><p>If the new <span>browsing context</span> has a <span>creator browsing context</span>,
-     then the <span>origin</span> of <var>document</var> the <span>origin</span> of the
-     <span>creator <code>Document</code></span>.</p></li>
+     then the <span>origin</span> of <var>document</var> is the <span>creator
+     origin</span>.</p></li>
 
      <li><p>Otherwise, the <span>origin</span> of <var>document</var> is a unique <span
      data-x="concept-origin-opaque">opaque origin</span> assigned when the new <span>browsing
      context</span> is created.</p></li>
     </ul>
    </li>
 
-   <li><p>If the new <span>browsing context</span> has a <span>creator
-   <code>Document</code></span>, then set <var>document</var>'s <span data-x="the document's
-   referrer">referrer</span> to <span data-x="the document's address">the address</span> of that
-   <span>creator <code>Document</code></span>.</p></li>
+   <li><p>If the new <span>browsing context</span> has a <span>creator browsing context</span>, then
+   set <var>document</var>'s <span data-x="the document's referrer">referrer</span> to the
+   <span>creator URL</span>.</p></li>
 
    <li><p>Ensure that <var>document</var> has a single child <code>html</code> node, which itself
    has two empty child nodes: a <code>head</code> element, and a <code>body</code>