Add a weak property type to the virtual machine.

runtime/vm/raw_object.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/raw_object.h"
 
 #include "vm/class_table.h"
 #include "vm/freelist.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 942 matching lines @@
 
 intptr_t RawJSRegExp::VisitJSRegExpPointers(RawJSRegExp* raw_obj,
                                             ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.
   ASSERT(raw_obj->IsHeapObject());
   intptr_t length = Smi::Value(raw_obj->ptr()->data_length_);
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
   return JSRegExp::InstanceSize(length);
 }
 
+
+intptr_t RawWeakProperty::VisitWeakPropertyPointers(
+    RawWeakProperty* raw_obj, ObjectPointerVisitor* visitor) {
+  // Make sure that we got here with the tagged pointer as this.
+  ASSERT(raw_obj->IsHeapObject());
+  visitor->VisitPointers(raw_obj->from(), raw_obj->to());
+  return WeakProperty::InstanceSize();
+}
+
 }  // namespace dart