Go through root to get loading clients in StyleSheetContents::checkLoaded.

Source/core/css/StyleSheetContents.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2012 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 373 matching lines @@
     // ScriptableDocumentParser::executeScriptsWaitingForResources().
     // See https://bugs.webkit.org/show_bug.cgi?id=95106
     RefPtrWillBeRawPtr<StyleSheetContents> protect(this);
 
     StyleSheetContents* parentSheet = parentStyleSheet();
     if (parentSheet) {
         parentSheet->checkLoaded();
         return;
     }
 
-    StyleSheetContents* root = rootStyleSheet();
-    if (root->m_loadingClients.isEmpty())
+    ASSERT(this == rootStyleSheet());
+    if (m_loadingClients.isEmpty())
         return;
 
     // Avoid |CSSSStyleSheet| and |ownerNode| being deleted by scripts that run via
     // ScriptableDocumentParser::executeScriptsWaitingForResources(). Also protect
     // the |CSSStyleSheet| from being deleted during iteration via the |sheetLoaded|
     // method.
     //
     // When a sheet is loaded it is moved from the set of loading clients
     // to the set of completed clients. We therefore need the copy in order to
     // not modify the set while iterating it.
@@ skipping 283 matching lines @@
     visitor->trace(m_ownerRule);
     visitor->trace(m_importRules);
     visitor->trace(m_childRules);
     visitor->trace(m_loadingClients);
     visitor->trace(m_completedClients);
     visitor->trace(m_ruleSet);
 #endif
 }
 
 }