Allow the list of type parameters in the default factory clause to be omitted.

runtime/vm/class_finalizer.cc

Index: runtime/vm/class_finalizer.cc
===================================================================
--- runtime/vm/class_finalizer.cc	(revision 3579)
+++ runtime/vm/class_finalizer.cc	(working copy)
@@ -405,7 +405,8 @@
       mismatch = true;
     }
   }
-  if (mismatch) {
+  // The list of type parameters in the default factory clause can be omitted.
+  if (mismatch && (num_type_params > 0)) {
     const String& interface_name = String::Handle(interface.Name());
     const String& factory_name = String::Handle(factory_class.Name());
     const Script& script = Script::Handle(interface.script());