Add a weak property type to the virtual machine.

runtime/vm/scavenger.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_SCAVENGER_H_
 #define VM_SCAVENGER_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
@@ skipping 76 matching lines @@
 
   void WriteProtect(bool read_only);
 
  private:
   uword FirstObjectStart() const { return to_->start() | object_alignment_; }
   void Prologue(Isolate* isolate, bool invoke_api_callbacks);
   void IterateStoreBuffers(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateRoots(Isolate* isolate,
                     ScavengerVisitor* visitor,
                     bool visit_prologue_weak_persistent_handles);
+  void IterateWeakProperties(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateWeakReferences(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateWeakRoots(Isolate* isolate,
                         HandleVisitor* visitor,
                         bool visit_prologue_weak_persistent_handles);
   void ProcessToSpace(ScavengerVisitor* visitor);
+  uword ProcessWeakProperty(RawWeakProperty* raw_weak,
+                            ScavengerVisitor* visitor);
   void Epilogue(Isolate* isolate, bool invoke_api_callbacks);
 
   bool IsUnreachable(RawObject** p);
 
   // During a scavenge we need to remember the promoted objects.
   // This is implemented as a stack of objects at the end of the to space. As
   // object sizes are always greater than sizeof(uword) and promoted objects do
   // not consume space in the to space they leave enough room for this stack.
   void PushToPromotedStack(uword addr) {
     end_ -= sizeof(addr);
@@ skipping 40 matching lines @@
 
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCAVENGER_H_