Remove #pragma once from sync

sync/test/sessions/test_scoped_session_event_listener.h

 // Copyright (c) 2012 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.
 
 #ifndef SYNC_TEST_SESSIONS_TEST_SCOPED_SESSION_EVENT_LISTENER_H_
 #define SYNC_TEST_SESSIONS_TEST_SCOPED_SESSION_EVENT_LISTENER_H_
-#pragma once
 
 #include "sync/sessions/sync_session_context.h"
 
 namespace syncer {
 namespace sessions {
 
 // Installs a SyncEventListener to a given session context for the lifetime of
 // the TestScopedSessionEventListener.
 class TestScopedSessionEventListener {
  public:
   TestScopedSessionEventListener(
       SyncSessionContext* context,
       SyncEngineEventListener* listener)
     : context_(context), listener_(listener) {
       context->listeners_.AddObserver(listener);
   }
   ~TestScopedSessionEventListener() {
     context_->listeners_.RemoveObserver(listener_);
   }
  private:
   SyncSessionContext* context_;
   SyncEngineEventListener* listener_;
   DISALLOW_COPY_AND_ASSIGN(TestScopedSessionEventListener);
 };
 
 }  // namespace sessions
 }  // namespace syncer
 
 #endif  // SYNC_TEST_SESSIONS_TEST_SCOPED_SESSION_EVENT_LISTENER_H_