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

base/sha1.h

 // Copyright (c) 2011 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_SHA1_H_
 #define BASE_SHA1_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 
 namespace base {
 
 // These functions perform SHA-1 operations.
 
 static const size_t kSHA1Length = 20;  // Length in bytes of a SHA-1 hash.
 
 // Computes the SHA-1 hash of the input string |str| and returns the full
 // hash.
 BASE_EXPORT std::string SHA1HashString(const std::string& str);
 
 // Computes the SHA-1 hash of the |len| bytes in |data| and puts the hash
 // in |hash|. |hash| must be kSHA1Length bytes long.
 BASE_EXPORT void SHA1HashBytes(const unsigned char* data, size_t len,
                                unsigned char* hash);
 
 }  // namespace base
 
 #endif  // BASE_SHA1_H_