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

base/linked_list.h

 // Copyright (c) 2009 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_LINKED_LIST_H_
 #define BASE_LINKED_LIST_H_
-#pragma once
 
 // Simple LinkedList type. (See the Q&A section to understand how this
 // differs from std::list).
 //
 // To use, start by declaring the class which will be contained in the linked
 // list, as extending LinkNode (this gives it next/previous pointers).
 //
 //   class MyNodeType : public LinkNode<MyNodeType> {
 //     ...
 //   };
@@ skipping 145 matching lines @@
     return &root_;
   }
 
  private:
   LinkNode<T> root_;
 };
 
 }  // namespace base
 
 #endif  // BASE_LINKED_LIST_H_