Support Dart optional arguments which are not dispatched, but instead use default values.

client/dom/scripts/databasebuilder.py

Index: client/dom/scripts/databasebuilder.py
diff --git a/client/dom/scripts/databasebuilder.py b/client/dom/scripts/databasebuilder.py
index 81d104682d64660c57c4a72805cd71b3f7db09d3..f0e2d55ee50c82d58c0694e0ab9e3df5a21be491 100755
--- a/client/dom/scripts/databasebuilder.py
+++ b/client/dom/scripts/databasebuilder.py
@@ -126,13 +126,19 @@ class DatabaseBuilder(object):
     for op in interface.operations:
       for i in range(0, len(op.arguments)):
         argument = op.arguments[i]
+
+        in_optional_whitelist = (interface.id, op.id, argument.id) in optional_argument_whitelist
+        if in_optional_whitelist or set(['Optional', 'Callback']).issubset(argument.ext_attrs.keys()):
+          argument.is_optional = True
+          argument.ext_attrs['RequiredCppParameter'] = None
+          continue
+
         if argument.is_optional:
           if 'Optional' in argument.ext_attrs:
             optional_value = argument.ext_attrs['Optional']
             if optional_value:
-              if (interface.id, op.id, argument.id) not in optional_argument_whitelist:
-                argument.is_optional = False
-                del argument.ext_attrs['Optional']
+              argument.is_optional = False
+              del argument.ext_attrs['Optional']
 
     # split operations with optional args into multiple operations
     new_ops = []