Add Observatory support for UnlinkedCall, SingleTargetCache and SubtypeTestCache.

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

Index: runtime/observatory/lib/src/models/objects/single_target_cache.dart
diff --git a/runtime/observatory/lib/src/models/objects/single_target_cache.dart b/runtime/observatory/lib/src/models/objects/single_target_cache.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5178e7ada4f1656f6e40a5162447e04403a988fb
--- /dev/null
+++ b/runtime/observatory/lib/src/models/objects/single_target_cache.dart
@@ -0,0 +1,15 @@
+// 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 SingleTargetCacheRef extends ObjectRef {
+  Code get target;
+}
+
+abstract class SingleTargetCache extends Object
+    implements SingleTargetCacheRef {
+  int get lowerLimit;
+  int get upperLimit;
+}