Implement weak persistent handles in the Dart API.

runtime/vm/isolate.h

 // 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include <limits.h>
 
 #include "include/dart_api.h"
@@ skipping 28 matching lines @@
   static inline Isolate* Current();
   static void SetCurrent(Isolate* isolate);
 
   static void InitOnce();
   static Isolate* Init();
   void Shutdown();
 
   // Visit all object pointers.
   void VisitObjectPointers(ObjectPointerVisitor* visitor, bool validate_frames);
 
+  void VisitStrongObjectPointers(ObjectPointerVisitor* visitor,
+                                 bool validate_frames);
+
+  void VisitWeakObjectPointers(ObjectPointerVisitor* visitor);
+
   StoreBufferBlock* store_buffer() { return &store_buffer_; }
 
   Dart_PostMessageCallback post_message_callback() const {
     return post_message_callback_;
   }
   void set_post_message_callback(Dart_PostMessageCallback value) {
     post_message_callback_ = value;
   }
 
   Dart_ClosePortCallback close_port_callback() const {
@@ skipping 253 matching lines @@
 #include "vm/isolate_linux.h"
 #elif defined(TARGET_OS_MACOS)
 #include "vm/isolate_macos.h"
 #elif defined(TARGET_OS_WINDOWS)
 #include "vm/isolate_win.h"
 #else
 #error Unknown target os.
 #endif
 
 #endif  // VM_ISOLATE_H_