Provide an Expando implementation for the VM.

runtime/lib/weak_property.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/bootstrap_natives.h"
 
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 
@@ skipping 15 matching lines @@
   arguments->SetReturn(key);
 }
 
 
 DEFINE_NATIVE_ENTRY(WeakProperty_getValue, 1) {
   GET_NATIVE_ARGUMENT(WeakProperty, weak_property, arguments->At(0));
   const Object& value = Object::Handle(weak_property.value());
   arguments->SetReturn(value);
 }
 
+
+DEFINE_NATIVE_ENTRY(WeakProperty_setValue, 2) {
+  GET_NATIVE_ARGUMENT(WeakProperty, weak_property, arguments->At(0));
+  GET_NATIVE_ARGUMENT(Instance, value, arguments->At(1));
+  weak_property.set_value(value);
+}
+
 }  // namespace dart