AU: Add support for reading the output of synchronous exec calls.

This will be used in a subsequent patch to invoke 'crossystem hwid' to read the
HWID.

BUG=chromium-os:15255
TEST=unit tests, tested AU on device

Change-Id: Ie26bae3621626d40f92f08e8549eefda77151102
Reviewed-on: http://gerrit.chromium.org/gerrit/1047
Reviewed-by: Thieu Le <thieule@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/delta_performer.cc b/delta_performer.cc
index 9978faf..6466795 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -517,8 +517,9 @@
   int return_code = 0;
   TEST_AND_RETURN_FALSE(
       Subprocess::SynchronousExecFlags(cmd,
+                                       G_SPAWN_LEAVE_DESCRIPTORS_OPEN,
                                        &return_code,
-                                       G_SPAWN_LEAVE_DESCRIPTORS_OPEN));
+                                       NULL));
   TEST_AND_RETURN_FALSE(return_code == 0);
 
   if (operation.dst_length() % block_size_) {