Turn isEmpty check in parseSimpleTransform into ASSERT

Source/core/css/parser/CSSParserFastPaths.cpp

Index: Source/core/css/parser/CSSParserFastPaths.cpp
diff --git a/Source/core/css/parser/CSSParserFastPaths.cpp b/Source/core/css/parser/CSSParserFastPaths.cpp
index d017a77870bbf4128dcf411fb4e10b6a5bfebaea..0245be5c86d1c4af936c788fc3101711962f229b 100644
--- a/Source/core/css/parser/CSSParserFastPaths.cpp
+++ b/Source/core/css/parser/CSSParserFastPaths.cpp
@@ -638,10 +638,10 @@ static PassRefPtrWillBeRawPtr<CSSValueList> parseSimpleTransformList(CharType*&
 
 static PassRefPtrWillBeRawPtr<CSSValue> parseSimpleTransform(CSSPropertyID propertyID, const String& string)
 {
+    ASSERT(!string.isEmpty());
+
     if (propertyID != CSSPropertyTransform)
         return nullptr;
-    if (string.isEmpty())
-        return nullptr;
     if (string.is8Bit()) {
         const LChar* pos = string.characters8();
         const LChar* end = pos + string.length();