Fix an MQ parsing related crash

Source/core/css/MediaQueryExp.cpp

Index: Source/core/css/MediaQueryExp.cpp
diff --git a/Source/core/css/MediaQueryExp.cpp b/Source/core/css/MediaQueryExp.cpp
index e1a4ffba4d5145b463c072da05d569937f8a955a..c85c928db4a67f0277d72cb1b020c758b661a9b9 100644
--- a/Source/core/css/MediaQueryExp.cpp
+++ b/Source/core/css/MediaQueryExp.cpp
@@ -214,6 +214,8 @@ MediaQueryExp::MediaQueryExp(const String& mediaFeature, PassRefPtrWillBeRawPtr<
 // FIXME - create should not return a null.
 PassOwnPtrWillBeRawPtr<MediaQueryExp> MediaQueryExp::create(const String& mediaFeature, CSSParserValueList* valueList)
 {
+    ASSERT(!mediaFeature.isNull());
+
     RefPtrWillBeRawPtr<CSSValue> cssValue;
     bool isValid = false;
     String lowerMediaFeature = attemptStaticStringCreation(mediaFeature.lower());
@@ -222,6 +224,7 @@ PassOwnPtrWillBeRawPtr<MediaQueryExp> MediaQueryExp::create(const String& mediaF
     if (valueList && valueList->size() > 0) {
         if (valueList->size() == 1) {
             CSSParserValue* value = valueList->current();
+            ASSERT(value);
 
             if (featureWithCSSValueID(lowerMediaFeature, value)) {
                 // Media features that use CSSValueIDs.