Disable expansion of VirtualTree and VirtualCollection items

runtime/observatory/lib/src/elements/helpers/any_ref.dart

Index: runtime/observatory/lib/src/elements/helpers/any_ref.dart
diff --git a/runtime/observatory/lib/src/elements/helpers/any_ref.dart b/runtime/observatory/lib/src/elements/helpers/any_ref.dart
index b7d6d08501cd5c20ffa7c3cad4edd8538829b57f..73064fd27d8d682b3839ad74a2d658d57f1c5ac6 100644
--- a/runtime/observatory/lib/src/elements/helpers/any_ref.dart
+++ b/runtime/observatory/lib/src/elements/helpers/any_ref.dart
@@ -29,12 +29,14 @@ import 'package:observatory/src/elements/unknown_ref.dart';
 import 'package:observatory/src/elements/unlinkedcall_ref.dart';
 
 Element anyRef(M.IsolateRef isolate, ref, M.ObjectRepository objects,
-    {RenderingQueue queue}) {
+    {RenderingQueue queue, bool expandable: true}) {
   if (ref is M.Guarded) {
     if (ref.isSentinel) {
-      return anyRef(isolate, ref.asSentinel, objects, queue: queue);
+      return anyRef(isolate, ref.asSentinel, objects,
+          queue: queue, expandable: expandable);
     } else {
-      return anyRef(isolate, ref.asValue, objects, queue: queue);
+      return anyRef(isolate, ref.asValue, objects,
+          queue: queue, expandable: expandable);
     }
   } else if (ref is M.ObjectRef) {
     if (ref is M.ClassRef) {
@@ -42,17 +44,20 @@ Element anyRef(M.IsolateRef isolate, ref, M.ObjectRepository objects,
     } else if (ref is M.CodeRef) {
       return new CodeRefElement(isolate, ref, queue: queue);
     } else if (ref is M.ContextRef) {
-      return new ContextRefElement(isolate, ref, objects, queue: queue);
+      return new ContextRefElement(isolate, ref, objects,
+          queue: queue, expandable: expandable);
     } else if (ref is M.Error) {
       return new ErrorRefElement(ref, queue: queue);
     } else if (ref is M.FieldRef) {
-      return new FieldRefElement(isolate, ref, objects, queue: queue);
+      return new FieldRefElement(isolate, ref, objects,
+          queue: queue, expandable: expandable);
     } else if (ref is M.FunctionRef) {
       return new FunctionRefElement(isolate, ref, queue: queue);
     } else if (ref is M.ICDataRef) {
       return new ICDataRefElement(isolate, ref, queue: queue);
     } else if (ref is M.InstanceRef) {
-      return new InstanceRefElement(isolate, ref, objects, queue: queue);
+      return new InstanceRefElement(isolate, ref, objects,
+          queue: queue, expandable: expandable);
     } else if (ref is M.LibraryRef) {
       return new LibraryRefElement(isolate, ref, queue: queue);
     } else if (ref is M.LocalVarDescriptorsRef) {