Use a tag bit for indicating prologue weak persistent handles, this avoids

runtime/vm/gc_marker.cc

 // Copyright (c) 2011, 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/gc_marker.h"
 
 #include <map>
 #include <utility>
 #include <vector>
 
@@ skipping 283 matching lines @@
   }
   return !raw_obj->IsMarked();
 }
 
 
 class MarkingWeakVisitor : public HandleVisitor {
  public:
   MarkingWeakVisitor() {
   }
 
-  void VisitHandle(uword addr) {
+  void VisitHandle(uword addr, bool is_prologue_weak) {
     FinalizablePersistentHandle* handle =
         reinterpret_cast<FinalizablePersistentHandle*>(addr);
     RawObject* raw_obj = handle->raw();
     if (IsUnreachable(raw_obj)) {
-      FinalizablePersistentHandle::Finalize(handle);
+      FinalizablePersistentHandle::Finalize(handle, is_prologue_weak);
     }
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MarkingWeakVisitor);
 };
 
 
 void GCMarker::Prologue(Isolate* isolate, bool invoke_api_callbacks) {
   if (invoke_api_callbacks) {
@@ skipping 177 matching lines @@
   MarkingWeakVisitor mark_weak;
   IterateWeakRoots(isolate, &mark_weak, invoke_api_callbacks);
   mark.Finalize();
   ProcessWeakTables(page_space);
   ProcessObjectIdTable(isolate);
 
   Epilogue(isolate, invoke_api_callbacks);
 }
 
 }  // namespace dart