Fixing custom element type extensions to have correct native type

Source/bindings/dart/DartUtilities.cpp

Index: Source/bindings/dart/DartUtilities.cpp
diff --git a/Source/bindings/dart/DartUtilities.cpp b/Source/bindings/dart/DartUtilities.cpp
index 8c39f886e158c51bf040faff84a42906d1587582..4edfbdb72ef5d4ea78e543912845d36999c5358b 100644
--- a/Source/bindings/dart/DartUtilities.cpp
+++ b/Source/bindings/dart/DartUtilities.cpp
@@ -395,21 +395,16 @@ bool DartUtilities::isTypeSubclassOf(Dart_Handle type, intptr_t libraryId, const
     return boolResult;
 }
 
-bool DartUtilities::isTypeSubclassOfTag(Dart_Handle type, const String& tagName)
+Dart_Handle DartUtilities::getAndValidateNativeType(Dart_Handle type, const String& tagName)
 {
     Dart_Handle args[2] = { type, stringToDartString(tagName) };
-    Dart_Handle result = DartUtilities::invokeUtilsMethod("isTypeSubclassOfTag", 2, args);
+    Dart_Handle result = DartUtilities::invokeUtilsMethod("getAndValidateNativeType", 2, args);
     ASSERT(!Dart_IsError(result));
     if (Dart_IsError(result)) {
         ASSERT_NOT_REACHED();
-        return false;
+        return Dart_Null();
     }
-
-    Dart_Handle exception = 0;
-    bool boolResult = dartToBool(result, exception);
-    if (exception)
-        return false;
-    return boolResult;
+    return result;
 }
 
 bool DartUtilities::isTypedData(Dart_Handle handle)