In background compilation make a copy of Field in order to freeze its state

runtime/vm/object_service.cc

Index: runtime/vm/object_service.cc
diff --git a/runtime/vm/object_service.cc b/runtime/vm/object_service.cc
index b71a58cbab53b211dfad4f57928aeba75a0ab988..ba631346ec4cb2192ad158767cf29faec4cf8ed7 100644
--- a/runtime/vm/object_service.cc
+++ b/runtime/vm/object_service.cc
@@ -334,7 +334,7 @@ void RedirectionData::PrintJSONImpl(JSONStream* stream, bool ref) const {
 
 void Field::PrintJSONImpl(JSONStream* stream, bool ref) const {
   JSONObject jsobj(stream);
-  Class& cls = Class::Handle(owner());
+  Class& cls = Class::Handle(Owner());
   String& field_name = String::Handle(name());
   field_name = String::EncodeIRI(field_name);
   AddCommonObjectProperties(&jsobj, "Field", ref);
@@ -382,8 +382,8 @@ void Field::PrintJSONImpl(JSONStream* stream, bool ref) const {
   } else {
     jsobj.AddProperty("_guardLength", guarded_list_length());
   }
-  const Class& origin_cls = Class::Handle(origin());
-  const Script& script = Script::Handle(origin_cls.script());
+  const Class& origin_cls = Class::Handle(Origin());
+  const class Script& script = Script::Handle(origin_cls.script());
   if (!script.IsNull()) {
     jsobj.AddLocation(script, token_pos());
   }