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

pkg/front_end/testcases/regress/issue_29982.dart

Index: pkg/front_end/testcases/regress/issue_29982.dart
diff --git a/pkg/front_end/testcases/regress/issue_29982.dart b/pkg/front_end/testcases/regress/issue_29982.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4108de0f995dc7fcee01f75b4ea2a3fa364f0846
--- /dev/null
+++ b/pkg/front_end/testcases/regress/issue_29982.dart
@@ -0,0 +1,8 @@
+// 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.
+
+main() {
+  var eh = {"éh": "éh"};
+  print('${eh[éh']}');
+}