Remove #pragma once from sync

sync/internal_api/public/util/immutable.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.
 
 // Immutable<T> provides an easy, cheap, and thread-safe way to pass
 // large immutable data around.
 //
 // For example, consider the following code:
 //
 //  typedef std::vector<LargeObject> LargeObjectList;
@@ skipping 46 matching lines @@
 // Alternatively, you could explicitly control which swap function is
 // used by providing your own traits class or using one of the
 // pre-defined ones below.  See comments on traits below for details.
 //
 // NOTE: Some complexity is necessary in order to use Immutable<T>
 // with forward-declared types.  See comments on traits below for
 // details.
 
 #ifndef SYNC_UTIL_IMMUTABLE_H_
 #define SYNC_UTIL_IMMUTABLE_H_
-#pragma once
 
 // For std::swap().
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 
 namespace syncer {
 
 namespace internal {
@@ skipping 175 matching lines @@
 
 // Helper function to avoid having to write out template arguments.
 template <typename T>
 Immutable<T> MakeImmutable(T* t) {
   return Immutable<T>(t);
 }
 
 }  // namespace syncer
 
 #endif  // SYNC_UTIL_IMMUTABLE_H_