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

base/environment.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_ENVIRONMENT_H_
 #define BASE_ENVIRONMENT_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 namespace base {
 
 namespace env_vars {
 
@@ skipping 22 matching lines @@
   virtual bool SetVar(const char* variable_name,
                       const std::string& new_value) = 0;
 
   // Returns true on success, otherwise returns false.
   virtual bool UnSetVar(const char* variable_name) = 0;
 };
 
 }  // namespace base
 
 #endif  // BASE_ENVIRONMENT_H_