Disallow repeated type parameters (issues 2239 & 2240).

tests/language/type_variable_scope3_test.dart

Index: tests/language/type_variable_scope3_test.dart
===================================================================
--- tests/language/type_variable_scope3_test.dart	(revision 0)
+++ tests/language/type_variable_scope3_test.dart	(revision 0)
@@ -0,0 +1,16 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test that a type parameter cannot be repeated.
+
+class Foo<T
+    , T  /// 00: compile-time error
+    > {
+}
+
+main() {
+  new Foo<String
+      , String  /// 00: continued
+      >();
+}