Tearing off a top-level variable introduces a synthetic field which is added to the top-level class…

runtime/vm/precompiler.cc

Index: runtime/vm/precompiler.cc
diff --git a/runtime/vm/precompiler.cc b/runtime/vm/precompiler.cc
index 22348eb43e4b6340e755c19115f1bbbfc7ab70ce..de1f3536e391dbdd84ff30d999390597e95790ae 100644
--- a/runtime/vm/precompiler.cc
+++ b/runtime/vm/precompiler.cc
@@ -1721,8 +1721,7 @@ void Precompiler::DropFields() {
           bool top_level = cls.IsTopLevel();
           if (top_level) {
             name = field.DictionaryName();
-            bool removed = lib.RemoveObject(field, name);
-            ASSERT(removed);
+            lib.RemoveObject(field, name);
           }
           dropped_field_count_++;
           if (FLAG_trace_precompiler) {