Fix serialization of alias_for properties

Source/core/css/CSSPrimitiveValue.cpp

Index: Source/core/css/CSSPrimitiveValue.cpp
diff --git a/Source/core/css/CSSPrimitiveValue.cpp b/Source/core/css/CSSPrimitiveValue.cpp
index 60b83526c917d22055691e2bc2febfba2c2f4563..cd62e28952a5d27259e64ab93a2e3c01690116d2 100644
--- a/Source/core/css/CSSPrimitiveValue.cpp
+++ b/Source/core/css/CSSPrimitiveValue.cpp
@@ -259,12 +259,6 @@ CSSPrimitiveValue::UnitType CSSPrimitiveValue::primitiveType() const
 
 static const AtomicString& propertyName(CSSPropertyID propertyID)
 {
-    ASSERT_ARG(propertyID, propertyID >= 0);
-    ASSERT_ARG(propertyID, (propertyID >= firstCSSProperty && propertyID < firstCSSProperty + numCSSProperties));
-
-    if (propertyID < 0)
-        return nullAtom;
-
     return getPropertyNameAtomicString(propertyID);
 }