Verify that correct number of arguments was passed.

tools/dom/scripts/systemnative.py

Index: tools/dom/scripts/systemnative.py
diff --git a/tools/dom/scripts/systemnative.py b/tools/dom/scripts/systemnative.py
index fb659f4c81da3904358c664a27421ee0d5acf49c..534121f74378f9654eab22a40e07c5c03a8cf65a 100644
--- a/tools/dom/scripts/systemnative.py
+++ b/tools/dom/scripts/systemnative.py
@@ -557,9 +557,9 @@ class DartiumBackend(HtmlDartGenerator):
       if not is_custom:
         self._GenerateOperationNativeCallback(operation, operation.arguments, cpp_callback_name)
     else:
-      self._GenerateDispatcher(info.operations, dart_declaration, [info.name for info in info.param_infos])
+      self._GenerateDispatcher(info.operations, info.NumberOfRequiredInDart(), dart_declaration, [info.name for info in info.param_infos])
 
-  def _GenerateDispatcher(self, operations, dart_declaration, parameter_names):
+  def _GenerateDispatcher(self, operations, number_of_required_in_dart, dart_declaration, parameter_names):
 
     def GenerateCall(
         stmts_emitter, call_emitter, version, operation, argument_count):
@@ -579,6 +579,7 @@ class DartiumBackend(HtmlDartGenerator):
     self._GenerateDispatcherBody(
         operations,
         parameter_names,
+        number_of_required_in_dart,
         dart_declaration,
         GenerateCall,
         self._IsArgumentOptionalInWebCore)