Add Observatory support for UnlinkedCall, SingleTargetCache and SubtypeTestCache.

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

Index: runtime/observatory/lib/src/models/repositories/single_target_cache.dart
diff --git a/runtime/observatory/lib/src/models/repositories/single_target_cache.dart b/runtime/observatory/lib/src/models/repositories/single_target_cache.dart
new file mode 100644
index 0000000000000000000000000000000000000000..bc4a767d17e3259c877614ebea7a8461e8ea542b
--- /dev/null
+++ b/runtime/observatory/lib/src/models/repositories/single_target_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 SingleTargetCacheRepository {
+  Future<SingleTargetCache> get(IsolateRef isolate, String id);
+}