Pass in the isolate parameter to the weak persistent callback handler so that

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
===================================================================
--- runtime/bin/dartutils.cc	(revision 33281)
+++ runtime/bin/dartutils.cc	(working copy)
@@ -1081,7 +1081,9 @@
 void CObject::FreeIOBufferData(Dart_CObject* cobject) {
   ASSERT(cobject->type == Dart_CObject_kExternalTypedData);
   cobject->value.as_external_typed_data.callback(
-      NULL, cobject->value.as_external_typed_data.peer);
+      NULL,
+      NULL,
+      cobject->value.as_external_typed_data.peer);
   cobject->value.as_external_typed_data.data = NULL;
 }