add weakcallback without persistent copying

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 7e7254aa33e6f5bd3291ac3347540d808f4fa4b5..f36c5ac7612bc6dfbc6098ca2154a1a15b2113f5 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -649,11 +649,11 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_Fix) {
 
 
 static void ArrayBufferWeakCallback(v8::Isolate* external_isolate,
-                                    Persistent<Value> object,
+                                    Persistent<Value>* object,
                                     void* data) {
   Isolate* isolate = reinterpret_cast<Isolate*>(external_isolate);
   HandleScope scope(isolate);
-  Handle<Object> internal_object = Utils::OpenHandle(*object);
+  Handle<Object> internal_object = Utils::OpenHandle(**object);
 
   size_t allocated_length = NumberToSize(
       isolate, JSArrayBuffer::cast(*internal_object)->byte_length());
@@ -661,7 +661,7 @@ static void ArrayBufferWeakCallback(v8::Isolate* external_isolate,
       -static_cast<intptr_t>(allocated_length));
   if (data != NULL)
     free(data);
-  object.Dispose(external_isolate);
+  object->Dispose(external_isolate);
 }