fixes #610, incorrect help output

lib/src/compiler/element_helpers.dart

Index: lib/src/compiler/element_helpers.dart
diff --git a/lib/src/compiler/element_helpers.dart b/lib/src/compiler/element_helpers.dart
index 5af5470fa11a0d8f7ebec7bc3624610ec38a0108..053227dfa8719f607e3946095dd487d67b9d467a 100644
--- a/lib/src/compiler/element_helpers.dart
+++ b/lib/src/compiler/element_helpers.dart
@@ -29,10 +29,9 @@ class Tuple2<T0, T1> {
 
 /*=T*/ fillDynamicTypeArgs/*<T extends DartType>*/(/*=T*/ t) {
   if (t is ParameterizedType) {
-    var pt = t as ParameterizedType;
     var dyn = new List<DartType>.filled(
-        pt.typeArguments.length, DynamicTypeImpl.instance);
-    return pt.substitute2(dyn, pt.typeArguments) as dynamic/*=T*/;
+        t.typeArguments.length, DynamicTypeImpl.instance);
+    return t.substitute2(dyn, t.typeArguments) as dynamic/*=T*/;
   }
   return t;
 }