Add language tests for Issue 18628.

tests/language/issue18628_2_test.dart

Index: tests/language/issue18628_2_test.dart
diff --git a/tests/language/issue18628_2_test.dart b/tests/language/issue18628_2_test.dart
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index 0000000000000000000000000000000000000000..c69b08cd8dcd5b805517e6585a17b05db44b7b92
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+++ b/tests/language/issue18628_2_test.dart
@@ -0,0 +1,13 @@
+// Copyright (c) 2014, 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.
+
+// This test checks for a regression found in Dart Editor: the
+// analyzer was treating [Type] as more specific than any type
+// variable (generic parameter).
+//
+// https://code.google.com/p/dart/issues/detail?id=18628
+
+class X<T extends Type> {}
+class Y<U> extends X<U> {} /// 01: static type warning
+main(){}