Implement prologue weak persistent handles.

runtime/vm/isolate.h

 // 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/thread.h"
@@ skipping 30 matching lines @@
     return reinterpret_cast<Isolate*>(Thread::GetThreadLocal(isolate_key));
   }
 
   static void SetCurrent(Isolate* isolate);
 
   static void InitOnce();
   static Isolate* Init(const char* name_prefix);
   void Shutdown();
 
   // Visit all object pointers.
-  void VisitObjectPointers(ObjectPointerVisitor* visitor, bool validate_frames);
+  void VisitObjectPointers(ObjectPointerVisitor* visitor,
+                           bool visit_prologue_weak_persistent_handles,
+                           bool validate_frames);
 
-  void VisitWeakPersistentHandles(HandleVisitor* visitor);
+  // Visits weak object pointers.
+  void VisitWeakPersistentHandles(HandleVisitor* visit,
+                                  bool visit_prologue_weak_persistent_handles);
 
   StoreBufferBlock* store_buffer() { return &store_buffer_; }
 
   Dart_MessageNotifyCallback message_notify_callback() const {
     return message_notify_callback_;
   }
   void set_message_notify_callback(Dart_MessageNotifyCallback value) {
     message_notify_callback_ = value;
   }
 
@@ skipping 223 matching lines @@
 
   static Dart_IsolateCreateCallback create_callback_;
   static Dart_IsolateInterruptCallback interrupt_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(Isolate);
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_