Remove uses of #pragma once and add PRESUBMIT check.

webrtc/examples/peerconnection/client/flagdefs.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_FLAGDEFS_H_
 #define WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_FLAGDEFS_H_
-#pragma once
 
 #include "webrtc/base/flags.h"
 
 extern const uint16_t kDefaultServerPort;  // From defaults.[h|cc]
 
 // Define flags for the peerconnect_client testing tool, in a separate
 // header file so that they can be shared across the different main.cc's
 // for each platform.
 
 DEFINE_bool(help, false, "Prints this message");
 DEFINE_bool(autoconnect, false, "Connect to the server without user "
                                 "intervention.");
 DEFINE_string(server, "localhost", "The server to connect to.");
 DEFINE_int(port, kDefaultServerPort,
            "The port on which the server is listening.");
 DEFINE_bool(autocall, false, "Call the first available other client on "
   "the server without user intervention.  Note: this flag should only be set "
   "to true on one of the two clients.");
 
 #endif  // WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_FLAGDEFS_H_