Fix an MQ parsing related crash

When MediaQueryParser used valuesList.clear(), clear() cleared the list's values, but not the offset of the current read value.
This fixes that.

BUG=353982

Review URL: https://codereview.chromium.org/204333005

git-svn-id: svn://svn.chromium.org/blink/trunk@169630 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/css/CSSParserValues.h

@@ -194,7 +194,7 @@ public:
 
     CSSParserValue* valueAt(unsigned i) { return i < m_values.size() ? &m_values[i] : 0; }
 
-    void clear() { m_values.clear(); }
+    void clear() { m_values.clear(); m_current = 0;}
 
 private:
     unsigned m_current;

third_party/WebKit/Source/core/css/CSSParserValuesTest.cpp

@@ -84,4 +84,17 @@ TEST(CSSParserValuesTest, EqualIgnoringCase16BitsString)
     ASSERT_FALSE(cssParserString.equalIgnoringCase("abCD"));
 }
 
+TEST(CSSParserValuesTest, CSSParserValuelistClear)
+{
+    CSSParserValueList list;
+    for (int i = 0; i < 3; ++i) {
+        CSSParserValue value;
+        value.setFromNumber(3);
+        list.addValue(value);
+    }
+    list.clear();
+    ASSERT_FALSE(list.size());
+    ASSERT_FALSE(list.currentIndex());
+}
+
 } // namespace

third_party/WebKit/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.