Handle owner state change in HTMLLinkElement::setCSSStyleSheet

Source/core/html/HTMLLinkElement.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, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 Google 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
@@ skipping 500 matching lines @@
     }
 
     // See the comment in ScriptLoader.cpp about why this check is necessary
     // here. https://crbug.com/500701.
     if (!cachedStyleSheet->errorOccurred() && !SubresourceIntegrity::CheckSubresourceIntegrity(*m_owner, cachedStyleSheet->sheetText(), KURL(baseURL, href), *cachedStyleSheet)) {
         m_loading = false;
         removePendingSheet();
         notifyLoadedSheetAndAllCriticalSubresources(Node::ErrorOccurredLoadingSubresource);
         return;
     }
-
+    // While the stylesheet is asynchronously loading, the owner can be moved under
+    // shadow tree.  In that case, cancel any processing on the loaded content.
+    if (m_owner->isInShadowTree()) {
+        m_loading = false;
+        removePendingSheet();
+        if (m_sheet)
+            clearSheet();
+        return;
+    }
     // Completing the sheet load may cause scripts to execute.
     RefPtrWillBeRawPtr<Node> protector(m_owner.get());
 
     CSSParserContext parserContext(m_owner->document(), 0, baseURL, charset);
 
     if (RefPtrWillBeRawPtr<StyleSheetContents> restoredSheet = const_cast<CSSStyleSheetResource*>(cachedStyleSheet)->restoreParsedStyleSheet(parserContext)) {
         ASSERT(restoredSheet->isCacheable());
         ASSERT(!restoredSheet->isLoading());
 
         if (m_sheet)
@@ skipping 238 matching lines @@
         removePendingSheet();
 }
 
 DEFINE_TRACE(LinkStyle)
 {
     visitor->trace(m_sheet);
     LinkResource::trace(visitor);
 }
 
 } // namespace blink