Make splash animations abort on scroll.

sky/engine/bindings/scripts/templates/interface_cpp.template

 {% extends 'interface_base_cpp.template' %}
 
 
 {# TODO(terry): Implement setter and deleter too #}
 
 
 {##############################################################################}
 {% block named_property_getter %}
 {% if named_property_getter and not named_property_getter.is_custom %}
 static void namedPropertyGetter(Dart_NativeArguments args)
@@ skipping 31 matching lines @@
     {{cpp_class}}* /* FIXME(vsm): Remove this. */ ALLOW_UNUSED receiver = GetReceiver<{{cpp_class}}>(args);
     Dart_Handle exception = nullptr;
     {
   {% if named_property_setter.is_raises_exception %}
         ExceptionState es;
   {% endif %}
 
         String name = DartConverter<String>::FromArguments(args, 1, exception);
         if (exception)
             goto fail;
-        String value = DartConverter<String>::FromArguments(args, 2, exception);
+        String value = DartConverter<String>::FromArgumentsWithNullCheck(args, 2, exception);
         if (exception)
             goto fail;
         {{named_property_setter.cpp_value}};
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
@@ skipping 172 matching lines @@
     return;
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 {% endif %}
 {% endblock %}
 
 
 {##############################################################################}