Remove uses of #pragma once and add PRESUBMIT check.

webrtc/examples/peerconnection/client/main_wnd.h

 /*
  *  Copyright 2012 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_MAIN_WND_H_
 #define WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_MAIN_WND_H_
-#pragma once
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/api/video/video_frame.h"
 #include "webrtc/base/win32.h"
 #include "webrtc/examples/peerconnection/client/peer_connection_client.h"
 #include "webrtc/media/base/mediachannel.h"
@@ skipping 169 matching lines @@
   MainWndCallback* callback_;
   static ATOM wnd_class_;
   std::string server_;
   std::string port_;
   bool auto_connect_;
   bool auto_call_;
 };
 #endif  // WIN32
 
 #endif  // WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_MAIN_WND_H_