Make the exception for ExecuteScript a regular Var instead of a VarPrivate.

ppapi/cpp/private/instance_private.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/cpp/private/instance_private.h"
 
 #include "ppapi/c/private/ppb_instance_private.h"
 #include "ppapi/c/private/ppp_instance_private.h"
 #include "ppapi/cpp/module_impl.h"
 #include "ppapi/cpp/private/var_private.h"
@@ skipping 46 matching lines @@
 }
 
 VarPrivate InstancePrivate::GetOwnerElementObject() {
   if (!has_interface<PPB_Instance_Private>())
     return VarPrivate();
   return VarPrivate(Var::PassRef(),
       get_interface<PPB_Instance_Private>()->GetOwnerElementObject(
           pp_instance()));
 }
 
-VarPrivate InstancePrivate::ExecuteScript(const Var& script,
-                                          VarPrivate* exception) {
+VarPrivate InstancePrivate::ExecuteScript(const Var& script, Var* exception) {
   if (!has_interface<PPB_Instance_Private>())
     return VarPrivate();
   return VarPrivate(Var::PassRef(),
              get_interface<PPB_Instance_Private>()->ExecuteScript(
                  pp_instance(),
                  script.pp_var(),
                  VarPrivate::OutException(exception).get()));
 }
 
 }  // namespace pp