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

runtime/vm/verifier.cc

 // Copyright (c) 2012, 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/verifier.h"
 
 #include "platform/assert.h"
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/freelist.h"
@@ skipping 21 matching lines @@
     if (raw_obj->IsHeapObject()) {
       if (!allocated_set_->Contains(raw_obj)) {
         uword raw_addr = RawObject::ToAddr(raw_obj);
         FATAL1("Invalid object pointer encountered %#" Px "\n", raw_addr);
       }
     }
   }
 }
 
 
-void VerifyWeakPointersVisitor::VisitHandle(uword addr) {
+void VerifyWeakPointersVisitor::VisitHandle(uword addr, bool is_prologue_weak) {
   FinalizablePersistentHandle* handle =
       reinterpret_cast<FinalizablePersistentHandle*>(addr);
   RawObject* raw_obj = handle->raw();
   visitor_->VisitPointer(&raw_obj);
 }
 
 
 void VerifyPointersVisitor::VerifyPointers() {
   NoGCScope no_gc;
   Isolate* isolate = Isolate::Current();
   ObjectSet* allocated_set = isolate->heap()->CreateAllocatedObjectSet();
   VerifyPointersVisitor visitor(isolate, allocated_set);
   // Visit all strongly reachable objects.
   isolate->VisitObjectPointers(&visitor,
                                false,  // skip prologue weak handles
                                StackFrameIterator::kValidateFrames);
   VerifyWeakPointersVisitor weak_visitor(&visitor);
   // Visit weak handles and prologue weak handles.
   isolate->VisitWeakPersistentHandles(&weak_visitor,
                                       true);  // visit prologue weak handles
   delete allocated_set;
 }
 
 }  // namespace dart