Add ImplementedBy attribute for operations merged from [Supplemental=XXX] interfaces.

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 a08857464747d67e97ced21e6485c02dffb7b26f..30d4e05b1e0cbf3efefd3176e9012ecfaa50815b 100755
--- a/client/dom/scripts/databasebuilder.py
+++ b/client/dom/scripts/databasebuilder.py
@@ -360,6 +360,11 @@ class DatabaseBuilder(object):
     def merge_list(what):
       old_list = old_interface.__dict__[what]
       new_list = new_interface.__dict__[what]
+
+      if what != 'parents' and old_interface.id != new_interface.id:
+        for node in new_list:
+          node.ext_attrs['ImplementedBy'] = new_interface.id
+
       changed = self._merge_nodes(old_list, new_list, import_options)
 
       # Delete list items with zero remaining annotations.