Improve HTMLScriptElement::didMoveToNewDocument() comment.

Source/core/html/HTMLScriptElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 57 matching lines @@
 void HTMLScriptElement::childrenChanged(const ChildrenChange& change)
 {
     HTMLElement::childrenChanged(change);
     m_loader->childrenChanged();
 }
 
 void HTMLScriptElement::didMoveToNewDocument(Document& oldDocument)
 {
     RefPtrWillBeRawPtr<Document> contextDocument = document().contextDocument().get();
     if (!contextDocument) {
+        // Document's contextDocument() method will return no Document if the
+        // following conditions both hold:
+        //
+        //   - The Document wasn't created with an explicit context document
+        //     and that document is otherwise kept alive.
+        //   - The Document itself is detached from its frame.
+        //
+        // The script element's loader is in that case moved to document() and
+        // its script runner, which is the non-null Document that contextDocument()
+        // would return if not detached.
         ASSERT(!document().frame());
-        // A frame-detached document is handled as having no context
-        // document - it would be the document if not detached. The
-        // newly moved script element needs to be the latter here as
-        // the script loader for the pending script must also move to
-        // reside with that document and its script runner.
         contextDocument = &document();
     }
     oldDocument.scriptRunner()->movePendingAsyncScript(contextDocument->scriptRunner(), m_loader.get());
     HTMLElement::didMoveToNewDocument(oldDocument);
 }
 
 void HTMLScriptElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     if (name == srcAttr)
         m_loader->handleSourceAttribute(value);
@@ skipping 127 matching lines @@
     return adoptRefWillBeNoop(new HTMLScriptElement(document(), false, m_loader->alreadyStarted()));
 }
 
 void HTMLScriptElement::trace(Visitor* visitor)
 {
     visitor->trace(m_loader);
     HTMLElement::trace(visitor);
 }
 
 }