Remove #pragma once. Just from base/ for now.

base/guid.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 BASE_GUID_H_
 #define BASE_GUID_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "build/build_config.h"
 
 namespace base {
 
 // Generate a 128-bit random GUID of the form: "%08X-%04X-%04X-%04X-%012llX".
 // If GUID generation fails an empty string is returned.
 // The POSIX implementation uses psuedo random number generation to create
 // the GUID.  The Windows implementation uses system services.
 BASE_EXPORT std::string GenerateGUID();
 
 // Returns true if the input string conforms to the GUID format.
 BASE_EXPORT bool IsValidGUID(const std::string& guid);
 
 #if defined(OS_POSIX)
 // For unit testing purposes only.  Do not use outside of tests.
 BASE_EXPORT std::string RandomDataToGUIDString(const uint64 bytes[2]);
 #endif
 
 }  // namespace guid
 
 #endif  // BASE_GUID_H_