Create local alias for super class in --closure mode (issue #312)

tool/input_sdk/private/types.dart

Index: tool/input_sdk/private/types.dart
diff --git a/tool/input_sdk/private/types.dart b/tool/input_sdk/private/types.dart
index d74be7190782067ac9f11ce947719fcb1498a979..25b1fe7408d29493c2476afca9d0ef5da6e3c038 100644
--- a/tool/input_sdk/private/types.dart
+++ b/tool/input_sdk/private/types.dart
@@ -38,8 +38,9 @@ final metadata = JS('', 'Symbol("metadata")');
 ///  String toString();
 ///
 ///
+final _TypeRepBase = JS('', '$LazyTagged(() => $Type)');
 final TypeRep = JS('', '''
-  class TypeRep extends $LazyTagged(() => $Type) {
+  class TypeRep extends $_TypeRepBase {
     get name() {return this.toString();}
   }
 ''');