Add Observatory support for UnlinkedCall, SingleTargetCache and SubtypeTestCache.

runtime/observatory/lib/src/models/repositories/subtype_test_cache.dart

Index: runtime/observatory/lib/src/models/repositories/subtype_test_cache.dart
diff --git a/runtime/observatory/lib/src/models/repositories/subtype_test_cache.dart b/runtime/observatory/lib/src/models/repositories/subtype_test_cache.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1a03805a02ffc44283cae0007e5e7544c47aa59b
--- /dev/null
+++ b/runtime/observatory/lib/src/models/repositories/subtype_test_cache.dart
@@ -0,0 +1,9 @@
+// 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
+
+part of models;
+
+abstract class SubtypeTestCacheRepository {
+  Future<SubtypeTestCache> get(IsolateRef isolate, String id);
+}