After detach, there's no document to notify parsing is finished.

third_party/WebKit/Source/core/html/HTMLViewSourceDocument.h

 /*
  * Copyright (C) 2006, 2008, 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef HTMLViewSourceDocument_h
 #define HTMLViewSourceDocument_h
 
+#include "core/CoreExport.h"
 #include "core/html/HTMLDocument.h"
 
 namespace blink {
 
 class HTMLTableCellElement;
 class HTMLTableSectionElement;
 class HTMLToken;
 
-class HTMLViewSourceDocument final : public HTMLDocument {
+class CORE_EXPORT HTMLViewSourceDocument final : public HTMLDocument {
  public:
   enum SourceAnnotation { AnnotateSourceAsSafe, AnnotateSourceAsXSS };
 
   static HTMLViewSourceDocument* create(const DocumentInit& initializer,
                                         const String& mimeType) {
     return new HTMLViewSourceDocument(initializer, mimeType);
   }
 
   void addSource(const String&, HTMLToken&, SourceAnnotation);
 
@@ skipping 34 matching lines @@
   String m_type;
   Member<Element> m_current;
   Member<HTMLTableSectionElement> m_tbody;
   Member<HTMLTableCellElement> m_td;
   int m_lineNumber;
 };
 
 }  // namespace blink
 
 #endif  // HTMLViewSourceDocument_h