Remove some Isolate::current_zone() calls, as it gets the zone from mutator thread not the current …

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index a92b4d5238092d1420dee86ed77dd614202bbf3d..4046041f5ba92ece4bc17a7ec4a136422f4902c4 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -2402,10 +2402,10 @@ void Debugger::CollectLibraryFields(const GrowableObjectArray& field_list,
                                     const String& prefix,
                                     bool include_private_fields) {
   DictionaryIterator it(lib);
-  Object& entry = Object::Handle(isolate_->current_zone());
+  Object& entry = Object::Handle(zone());
   Field& field = Field::Handle(zone());
   String& field_name = String::Handle(zone());
-  PassiveObject& field_value = PassiveObject::Handle(isolate_->current_zone());
+  PassiveObject& field_value = PassiveObject::Handle(zone());
   while (it.HasNext()) {
     entry = it.GetNext();
     if (entry.IsField()) {
@@ -2789,7 +2789,6 @@ void Debugger::Initialize(Isolate* isolate) {
     return;
   }
   isolate_ = isolate;
-
   // Use the isolate's control port as the isolate_id for debugging.
   // This port will be used as a unique ID to represent the isolate in the
   // debugger wire protocol messages.