[Mojo] Fix race condition in sample_app's SwapBuffers

mojo/examples/sample_app/native_viewport_client_impl.cc

 // Copyright 2013 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/examples/sample_app/native_viewport_client_impl.h"
 
 #include <stdio.h>
 
 #include "mojo/public/bindings/gles2_client/gles2_client_impl.h"
 
 namespace mojo {
 namespace examples {
 
 NativeViewportClientImpl::NativeViewportClientImpl(ScopedMessagePipeHandle pipe)
     : service_(pipe.Pass()) {
   service_.SetPeer(this);
 }
 
 NativeViewportClientImpl::~NativeViewportClientImpl() {
+  service_->Close();
 }
 
 void NativeViewportClientImpl::Open() {
   service_->Open();
 
   ScopedMessagePipeHandle gles2;
   ScopedMessagePipeHandle gles2_client;
   CreateMessagePipe(&gles2, &gles2_client);
 
   gles2_client_.reset(new GLES2ClientImpl(&gles2_delegate_, gles2.Pass()));
   service_->CreateGLES2Context(gles2_client.release());
 }
 
 void NativeViewportClientImpl::DidOpen() {
 }
 
 }  // namespace examples
 }  // namespace mojo