Check for null selectors when looping in findBestRuleSetAndAdd

Source/core/css/RuleSet.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 159 matching lines @@
     AtomicString id;
     AtomicString className;
     AtomicString customPseudoElementName;
     AtomicString tagName;
 
 #ifndef NDEBUG
     m_allRules.append(ruleData);
 #endif
 
     const CSSSelector* it = &component;
-    for (; it->relation() == CSSSelector::SubSelector; it = it->tagHistory()) {
+    for (; it && it->relation() == CSSSelector::SubSelector; it = it->tagHistory()) {
         extractValuesforSelector(it, id, className, customPseudoElementName, tagName);
     }
-    extractValuesforSelector(it, id, className, customPseudoElementName, tagName);
+    // FIXME: this null check should not be necessary. See crbug.com/358475
+    if (it)
+        extractValuesforSelector(it, id, className, customPseudoElementName, tagName);
 
     // Prefer rule sets in order of most likely to apply infrequently.
     if (!id.isEmpty()) {
         addToRuleSet(id, ensurePendingRules()->idRules, ruleData);
         return true;
     }
     if (!className.isEmpty()) {
         addToRuleSet(className, ensurePendingRules()->classRules, ruleData);
         return true;
     }
@@ skipping 212 matching lines @@
 
 #ifndef NDEBUG
 void RuleSet::show()
 {
     for (WillBeHeapVector<RuleData>::const_iterator it = m_allRules.begin(); it != m_allRules.end(); ++it)
         it->selector().show();
 }
 #endif
 
 } // namespace WebCore