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

base/mac/scoped_nsexception_enabler.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_MAC_SCOPED_NSEXCEPTION_ENABLER_H_
 #define BASE_MAC_SCOPED_NSEXCEPTION_ENABLER_H_
-#pragma once
 
 #import <Foundation/Foundation.h>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 
 namespace base {
 namespace mac {
 
 // BrowserCrApplication attempts to restrict throwing of NSExceptions
@@ skipping 27 matching lines @@
 
 // Executes [target performSelector:sel] with fatal-exceptions turned
 // off, and returns the result.  If an exception is thrown during the
 // perform, nil is returned.
 BASE_EXPORT id PerformSelectorIgnoringExceptions(NSObject* target, SEL sel);
 
 }  // namespace mac
 }  // namespace base
 
 #endif  // BASE_MAC_SCOPED_NSEXCEPTION_ENABLER_H_