Implement weak persistent handles in the Dart API.

runtime/vm/scavenger.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_SCAVENGER_H_
 #define VM_SCAVENGER_H_
 
 #include "vm/globals.h"
 #include "vm/object.h"
 #include "vm/utils.h"
@@ skipping 52 matching lines @@
   static intptr_t end_offset() { return OFFSET_OF(Scavenger, end_); }
 
   intptr_t in_use() const { return (top_ - FirstObjectStart()); }
 
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
  private:
   uword FirstObjectStart() const { return to_->start() | object_alignment_; }
   void Prologue();
   void IterateRoots(Isolate* isolate, ObjectPointerVisitor* visitor);
+  void IterateWeakRoots(Isolate* isolate, ObjectPointerVisitor* visitor);
   void ProcessToSpace(ObjectPointerVisitor* visitor);
   void Epilogue();
 
   VirtualMemory* space_;
   MemoryRegion* to_;
   MemoryRegion* from_;
 
   Heap* heap_;
 
   // Current allocation top and end. These values are being accessed directly
   // from generated code.
   uword top_;
   uword end_;
 
   // All object are aligned to this value.
   uword object_alignment_;
 
   // Scavenge cycle count.
   int count_;
   // Keep track whether a scavenge is currently running.
   bool scavenging_;
 
   friend class ScavengerVisitor;
+  friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCAVENGER_H_