Unify null treatment.

lib/dom/templates/dom/native/cpp_callback_header.template

Index: lib/dom/templates/dom/native/cpp_callback_header.template
diff --git a/lib/dom/templates/dom/native/cpp_callback_header.template b/lib/dom/templates/dom/native/cpp_callback_header.template
index d5b6a53b15cd525ace776270b770056c96538fe5..438d36e7be732043a0c5c5a75f81844cb9b39f51 100644
--- a/lib/dom/templates/dom/native/cpp_callback_header.template
+++ b/lib/dom/templates/dom/native/cpp_callback_header.template
@@ -18,12 +18,17 @@ class Dart$(INTERFACE) : public $(INTERFACE), public ActiveDOMCallback {
 public:
     typedef $(INTERFACE) NativeType;
 
-    static PassRefPtr<NativeType> create(Dart_Handle object, DartUtilities::ConversionFlag flag, Dart_Handle& exception)
+    static PassRefPtr<NativeType> create(Dart_Handle object, Dart_Handle& exception)
     {
-        if (flag == DartUtilities::ConvertNullToDefaultValue && Dart_IsNull(object))
-            return 0;
         return adoptRef(new Dart$(INTERFACE)(object, exception, DartUtilities::scriptExecutionContext()));
     }
+
+    static PassRefPtr<NativeType> createWithNullCheck(Dart_Handle object, Dart_Handle& exception)
+    {
+        if (Dart_IsNull(object))
+            return 0;
+        return create(object, exception);
+    }
 $HANDLERS
 
 private: