Check not to insert nullptr to HeapHashSet<WeakMember>

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 42 matching lines @@
   DCHECK(m_document->frame());
   FontCache::fontCache()->addClient(this);
   FontFaceSet::from(*document)->addFontFacesToFontFaceCache(&m_fontFaceCache,
                                                             this);
 }
 
 CSSFontSelector::~CSSFontSelector() {}
 
 void CSSFontSelector::registerForInvalidationCallbacks(
     CSSFontSelectorClient* client) {
+  CHECK(client);
   m_clients.insert(client);
 }
 
 void CSSFontSelector::unregisterForInvalidationCallbacks(
     CSSFontSelectorClient* client) {
   m_clients.erase(client);
 }
 
 void CSSFontSelector::dispatchInvalidationCallbacks() {
   m_fontFaceCache.incrementVersion();
@@ skipping 100 matching lines @@
 }
 
 DEFINE_TRACE(CSSFontSelector) {
   visitor->trace(m_document);
   visitor->trace(m_fontFaceCache);
   visitor->trace(m_clients);
   FontSelector::trace(visitor);
 }
 
 }  // namespace blink