During a reload, give const fields their new values.

runtime/vm/object_reload.cc

 // Copyright (c) 2016, 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 "vm/hash_table.h"
 #include "vm/isolate_reload.h"
 #include "vm/log.h"
 #include "vm/resolver.h"
@@ skipping 110 matching lines @@
   for (intptr_t i = 0; i < field_list.Length(); i++) {
     field = Field::RawCast(field_list.At(i));
     name = field.name();
     if (field.is_static()) {
       // Find the corresponding old field, if it exists, and migrate
       // over the field value.
       for (intptr_t j = 0; j < old_field_list.Length(); j++) {
         old_field = Field::RawCast(old_field_list.At(j));
         old_name = old_field.name();
         if (name.Equals(old_name)) {
-          if (update_values) {
+          // We only copy values if requested and if the field is not a const
+          // field. We let const fields be updated with a reload.
+          if (update_values && !field.is_const()) {
             value = old_field.StaticValue();
             field.SetStaticValue(value);
           }
           reload_context->AddStaticFieldMapping(old_field, field);
         }
       }
     }
   }
 }
 
@@ skipping 614 matching lines @@
       const Array& data_array =
           Array::Handle(zone, CachedEmptyICDataArray(num_args));
       set_ic_data_array(data_array);
     }
   }
 }
 
 #endif  // !PRODUCT
 
 }   // namespace dart.