Fix assert on unknown rule type in the BisonCSSParser::endRuleHeader.

Source/core/css/parser/BisonCSSParser-in.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 1992 matching lines @@
     m_ruleHeaderStartLineNumber = m_tokenizer.m_tokenStartLineNumber;
     if (m_observer) {
         ASSERT(!m_ruleHasHeader);
         m_observer->startRuleHeader(ruleType, m_ruleHeaderStartOffset);
         m_ruleHasHeader = true;
     }
 }
 
 void BisonCSSParser::endRuleHeader()
 {
-    ASSERT(m_ruleHeaderType != CSSRuleSourceData::UNKNOWN_RULE);
+    if (m_ruleHeaderType == CSSRuleSourceData::UNKNOWN_RULE)

[Julien - ping for review, 2014/06/06 20:13:06]

I don't think it's the right fix: we shouldn't be calling endRuleHeader without
a matching startRuleHeader and this ASSERT is preventing us from doing that.

The issue is in CSSGrammar.y where we are missing an invalid rule for @media
that would call endInvalidRuleHeader.

+        return;
+
     m_ruleHeaderType = CSSRuleSourceData::UNKNOWN_RULE;
     if (m_observer) {
         ASSERT(m_ruleHasHeader);
         m_observer->endRuleHeader(m_tokenizer.safeUserStringTokenOffset());
     }
 }
 
 void BisonCSSParser::startSelector()
 {
     if (m_observer)
@@ skipping 45 matching lines @@
     rule->setProperties(createStylePropertySet());
     clearProperties();
 
     StyleRuleViewport* result = rule.get();
     m_parsedRules.append(rule.release());
 
     return result;
 }
 
 }