Migrate language/arithmetic2_test ... language/async_await_syntax_test.

tests/language_2/assign_to_type_test.dart

+// Copyright (c) 2015, 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.
+
+// Verify that an attempt to assign to a class, enum, typedef, or type
+// parameter produces a compile error.
+
+class C<T> {
+  f() {
+    T = null; //# 01: compile-time error
+  }
+}
+
+class D {}
+
+enum E { e0 }
+
+typedef void F();
+
+main() {
+  new C<D>().f();
+  D = null; //# 02: compile-time error
+  E = null; //# 03: compile-time error
+  F = null; //# 04: compile-time error
+}