Add regression tests from Luke's bug reports. Part 1.

pkg/front_end/testcases/regress/issue_29981.dart

Index: pkg/front_end/testcases/regress/issue_29981.dart
diff --git a/pkg/front_end/testcases/regress/issue_29981.dart b/pkg/front_end/testcases/regress/issue_29981.dart
new file mode 100644
index 0000000000000000000000000000000000000000..354f8ce7c4ad2a8e1b151ba12e02664e17923a1c
--- /dev/null
+++ b/pkg/front_end/testcases/regress/issue_29981.dart
@@ -0,0 +1,11 @@
+// Copyright (c) 2017, 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.
+
+class C<T> {
+  C<String, String> field;
+}
+
+main() {
+  print(new C());
+}