Sever HTMLImportChild client connection upon disposal.

Source/core/html/imports/HTMLImportChild.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 40 matching lines @@
     , m_loader(loader)
     , m_client(nullptr)
 {
 }
 
 HTMLImportChild::~HTMLImportChild()
 {
 #if !ENABLE(OILPAN)
     // dispose() should be called before the destruction.
     ASSERT(!m_loader);
-
-    if (m_client)
-        m_client->importChildWasDestroyed(this);
 #endif
 }
 
 void HTMLImportChild::ownerInserted()
 {
     if (!m_loader->isDone())
         return;
     root()->document()->styleResolverChanged();
 }
 
@@ skipping 27 matching lines @@
 }
 
 void HTMLImportChild::dispose()
 {
     if (parent())
         parent()->removeChild(this);
 
     ASSERT(m_loader);
     m_loader->removeImport(this);
     m_loader = nullptr;
+
+    if (m_client) {
+        m_client->importChildWasDisposed(this);
+        m_client = nullptr;
+    }
 }
 
 Document* HTMLImportChild::document() const
 {
     ASSERT(m_loader);
     return m_loader->document();
 }
 
 void HTMLImportChild::stateWillChange()
 {
@@ skipping 100 matching lines @@
 
 DEFINE_TRACE(HTMLImportChild)
 {
     visitor->trace(m_customElementMicrotaskStep);
     visitor->trace(m_loader);
     visitor->trace(m_client);
     HTMLImport::trace(visitor);
 }
 
 } // namespace blink