Treat null like the object it is in the Observatory and Service.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index f0d805932409426e298832c5ab0ad44bb94ec61a..43d45935dd1a93a3298f678055c7787ad6fff78a 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -1549,6 +1549,11 @@ void Object::PrintJSON(JSONStream* stream, bool ref) const {
     jsobj.AddProperty("type", ref ? "@Null" : "Null");
     jsobj.AddProperty("id", "objects/null");
     jsobj.AddProperty("valueAsString", "null");
+    if (!ref) {
+      const Class& cls = Class::Handle(this->clazz());
+      jsobj.AddProperty("class", cls);
+      jsobj.AddProperty("size", raw()->Size());
+    }
   } else {
     PrintJSONImpl(stream, ref);
   }