Teach the Observatory about Contexts. Factor out object graph information from the instance view.

runtime/bin/vmservice/observatory/lib/src/elements/context_ref.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.
+
+library context_ref_element;
+
+import 'package:polymer/polymer.dart';
+import 'package:observatory/service.dart';
+import 'service_ref.dart';
+
+@CustomTag('context-ref')
+class ContextRefElement extends ServiceRefElement {
+  ContextRefElement.created() : super.created();
+
+  // TODO(turnidge): This is here to workaround vm/dart2js differences.
+  dynamic expander() {
+    return expandEvent;
+  }
+
+  void expandEvent(bool expand, Function onDone) {
+    assert(ref is Context);
+    if (expand) {
+      ref.reload().then((result) {
+        ref = result;
+        notifyPropertyChange(#ref, 0, 1);
+      }).whenComplete(onDone);
+    } else {
+      Context refMap = ref;
+      refMap.elements = null;
+      onDone();
+    }
+  }
+}