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

base/auto_reset.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_AUTO_RESET_H_
 #define BASE_AUTO_RESET_H_
-#pragma once
 
 #include "base/basictypes.h"
 
 // AutoReset<> is useful for setting a variable to a new value only within a
 // particular scope. An AutoReset<> object resets a variable to its original
 // value upon destruction, making it an alternative to writing "var = false;"
 // or "var = old_val;" at all of a block's exit points.
 //
 // This should be obvious, but note that an AutoReset<> instance should have a
 // shorter lifetime than its scoped_variable, to prevent invalid memory writes
@@ skipping 11 matching lines @@
   ~AutoReset() { *scoped_variable_ = original_value_; }
 
  private:
   T* scoped_variable_;
   T original_value_;
 
   DISALLOW_COPY_AND_ASSIGN(AutoReset);
 };
 
 #endif  // BASE_AUTO_RESET_H_