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

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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/isolate.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
 #include "platform/text_buffer.h"
@@ skipping 2064 matching lines @@
 }
 
 
 void Isolate::set_registered_service_extension_handlers(
     const GrowableObjectArray& value) {
   registered_service_extension_handlers_ = value.raw();
 }
 
 
 void Isolate::AddDeoptimizingBoxedField(const Field& field) {
+  ASSERT(field.IsOriginal());
   MonitorLocker ml(boxed_field_list_monitor_);
   if (boxed_field_list_ == GrowableObjectArray::null()) {
     boxed_field_list_ = GrowableObjectArray::New(Heap::kOld);
   }
   const GrowableObjectArray& array =
       GrowableObjectArray::Handle(boxed_field_list_);
   array.Add(field, Heap::kOld);
 }
 
 
@@ skipping 714 matching lines @@
 void IsolateSpawnState::DecrementSpawnCount() {
   ASSERT(spawn_count_monitor_ != NULL);
   ASSERT(spawn_count_ != NULL);
   MonitorLocker ml(spawn_count_monitor_);
   ASSERT(*spawn_count_ > 0);
   *spawn_count_ = *spawn_count_ - 1;
   ml.Notify();
 }
 
 }  // namespace dart