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

third_party/WebKit/Source/core/html/parser/HTMLViewSourceParser.cpp

 /*
  * Copyright (C) 2010 Google, 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
@@ skipping 59 matching lines @@
 
 void HTMLViewSourceParser::append(const String& input) {
   m_input.appendToEnd(input);
   pumpTokenizer();
 }
 
 void HTMLViewSourceParser::finish() {
   if (!m_input.haveSeenEndOfFile())
     m_input.markEndOfFile();
 
-  if (!isDetached())
+  if (!isDetached()) {
     pumpTokenizer();
-
-  document()->finishedParsing();
+    document()->finishedParsing();
+  }
 }
 
 }  // namespace blink