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

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

Index: Source/core/css/parser/BisonCSSParser-in.cpp
diff --git a/Source/core/css/parser/BisonCSSParser-in.cpp b/Source/core/css/parser/BisonCSSParser-in.cpp
index add82fdaf1d377746676bde932d0c69ba0c95e40..345d96023333c477d5abae7b236c323fc4baa5e3 100644
--- a/Source/core/css/parser/BisonCSSParser-in.cpp
+++ b/Source/core/css/parser/BisonCSSParser-in.cpp
@@ -2010,7 +2010,9 @@ void BisonCSSParser::startRuleHeader(CSSRuleSourceData::Type ruleType)
 
 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);