Speculatively handle weak member clearing while creating iteration vector.

third_party/WebKit/Source/core/css/CSSFontSelector.cpp

 /*
  * Copyright (C) 2007, 2008, 2011 Apple Inc. All rights reserved.
  *           (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * 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
@@ skipping 65 matching lines @@
     m_clients.remove(client);
 }
 #endif
 
 void CSSFontSelector::dispatchInvalidationCallbacks()
 {
     m_fontFaceCache.incrementVersion();
 
     WillBeHeapVector<RawPtrWillBeMember<CSSFontSelectorClient>> clients;
     copyToVector(m_clients, clients);
-    for (size_t i = 0; i < clients.size(); ++i)
-        clients[i]->fontsNeedUpdate(this);
+    // TODO(sof): the null check is temporarily in place to speculatively address
+    // crbug.com/568173.
+    for (auto& client : clients) {
+        if (client)
+            client->fontsNeedUpdate(this);
+    }
 }
 
 void CSSFontSelector::fontFaceInvalidated()
 {
     dispatchInvalidationCallbacks();
 }
 
 void CSSFontSelector::fontCacheInvalidated()
 {
     dispatchInvalidationCallbacks();
@@ skipping 87 matching lines @@
 #if ENABLE(OILPAN)
     visitor->trace(m_document);
     visitor->trace(m_fontFaceCache);
     visitor->trace(m_clients);
     visitor->trace(m_fontLoader);
 #endif
     FontSelector::trace(visitor);
 }
 
 } // namespace blink