Do not merge IDL interfaces in dartdomgenerator.

lib/dom/scripts/dartgenerator.py

Index: lib/dom/scripts/dartgenerator.py
diff --git a/lib/dom/scripts/dartgenerator.py b/lib/dom/scripts/dartgenerator.py
index a2338bbf0b35a1d7058097361332efb35a2571cc..c446486d6be565472b57f9dcce0f6d8e3242707d 100755
--- a/lib/dom/scripts/dartgenerator.py
+++ b/lib/dom/scripts/dartgenerator.py
@@ -80,13 +80,10 @@ class DartGenerator(object):
       if database.HasInterface(old_name):
         _logger.info('renaming interface %s to %s' % (old_name, new_name))
         interface = database.GetInterface(old_name)
-        database.DeleteInterface(old_name)
         if not database.HasInterface(new_name):
           interface.id = new_name
+          database.DeleteInterface(old_name)
           database.AddInterface(interface)
-        else:
-          new_interface = database.GetInterface(new_name)
-          MergeNodes(new_interface, interface)
 
         if rename_javascript_binding_names:
           interface.javascript_binding_name = new_name