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

Source/core/css/MediaQuerySetTest.cpp

Index: Source/core/css/MediaQuerySetTest.cpp
diff --git a/Source/core/css/MediaQuerySetTest.cpp b/Source/core/css/MediaQuerySetTest.cpp
index 834625e3ece81d36f0b7c96412861d1a7494289a..61616cd50a31001dba4ea24098dc860e1ee73adf 100644
--- a/Source/core/css/MediaQuerySetTest.cpp
+++ b/Source/core/css/MediaQuerySetTest.cpp
@@ -157,6 +157,8 @@ TEST(MediaQuerySetTest, Basic)
         {"'\"\"\"', (max-width: 900px)", "not all, (max-width: 900px)", true},
         {"\"'\"', (max-width: 900px)", "not all", true},
         {"\"'''\", (max-width: 900px)", "not all, (max-width: 900px)", true},
+        {"s}", "not all", true},
+        {"s}, (color)", "not all, (color)", true},
         {0, 0} // Do not remove the terminator line.
     };