Use HasResolvedTypeClass to avoid crash in Field::PrintToJSONStream.

runtime/vm/object.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 6379 matching lines @@
   jsobj.AddProperty("type", JSONType(ref));
   jsobj.AddPropertyF("id", "classes/%" Pd "/fields/%" Pd "", cid, id);
   jsobj.AddProperty("name", internal_field_name);
   jsobj.AddProperty("user_name", field_name);
   if (is_static()) {
     const Instance& valueObj = Instance::Handle(value());
     jsobj.AddProperty("value", valueObj);
   }
 
   jsobj.AddProperty("owner", cls);
+
+  // TODO(turnidge): Once the vmservice supports returning types,
+  // return the type here instead of the class.
   AbstractType& declared_type = AbstractType::Handle(type());
-  cls = declared_type.type_class();
-  jsobj.AddProperty("declared_type", cls);
+  if (declared_type.HasResolvedTypeClass()) {
+    cls = declared_type.type_class();
+    jsobj.AddProperty("declared_type", cls);
+  }
+
   jsobj.AddProperty("static", is_static());
   jsobj.AddProperty("final", is_final());
   jsobj.AddProperty("const", is_const());
   if (ref) {
     return;
   }
   jsobj.AddProperty("guard_nullable", is_nullable());
   if (guarded_cid() == kIllegalCid) {
     jsobj.AddProperty("guard_class", "unknown");
   } else if (guarded_cid() == kDynamicCid) {
@@ skipping 11085 matching lines @@
   return "_MirrorReference";
 }
 
 
 void MirrorReference::PrintToJSONStream(JSONStream* stream, bool ref) const {
   Instance::PrintToJSONStream(stream, ref);
 }
 
 
 }  // namespace dart