Fix bug 11637:

tests/language/private_mixin_exception_throw_test.dart

+// Copyright (c) 2013, 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.
+
+// Regression test for http://dartbug.com/11637
+
+class _C {}
+class _E {
+  throwIt() => throw "it";
+}
+class _F {
+  throwIt() => throw "IT";
+}
+class _D extends _C with _E, _F {}
+
+main() {
+  var d = new _D();
+  try {
+    d.throwIt();
+  } catch (e, s) {
+    print("Exception: $e");
+    print("Stacktrace:\n$s");
+  }
+}