Revert "Updating the mapped_file_avoid_mmap_posix implementation."

net/disk_cache/mapped_file.h

 // Copyright (c) 2012 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.
 
 // See net/disk_cache/disk_cache.h for the public interface of the cache.
 
 #ifndef NET_DISK_CACHE_MAPPED_FILE_H_
 #define NET_DISK_CACHE_MAPPED_FILE_H_
 
 #include "net/base/net_export.h"
@@ skipping 32 matching lines @@
 
  private:
   virtual ~MappedFile();
 
   bool init_;
 #if defined(OS_WIN)
   HANDLE section_;
 #endif
   void* buffer_;  // Address of the memory mapped buffer.
   size_t view_size_;  // Size of the memory pointed by buffer_.
+#if defined(POSIX_AVOID_MMAP)
+  void* snapshot_;  // Copy of the buffer taken when it was last flushed.
+#endif
 
   DISALLOW_COPY_AND_ASSIGN(MappedFile);
 };
 
 // Helper class for calling Flush() on exit from the current scope.
 class ScopedFlush {
  public:
   explicit ScopedFlush(MappedFile* file) : file_(file) {}
   ~ScopedFlush() {
     file_->Flush();
   }
  private:
   MappedFile* file_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_MAPPED_FILE_H_