Mojo: Add leak detection to mojo::embedder::test::Shutdown().

mojo/system/embedder/embedder_unittest.cc

 // Copyright 2014 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 "mojo/system/embedder/embedder.h"
 
 #include <string.h>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 73 matching lines @@
                                 base::Bind(&DestroyChannelOnIOThread,
                                            server_channel_info));
 
   EXPECT_TRUE(client_channel_info != NULL);
   system::test::PostTaskAndWait(io_thread_task_runner(),
                                 FROM_HERE,
                                 base::Bind(&DestroyChannelOnIOThread,
                                            client_channel_info));
 #endif  // !defined(OS_WIN)
 
-  test::Shutdown();
+  EXPECT_TRUE(test::Shutdown());
 }
 
 // TODO(vtl): Test immediate write & close.
 // TODO(vtl): Test broken-connection cases.
 
 }  // namespace
 }  // namespace embedder
 }  // namespace mojo