Clean up arena API

Summary:
Easy thing goes first. This patch moves arena to internal dir; based
on which, the coming patch will deal with memtable_rep.

Test Plan: make check

Reviewers: haobo, sdong, dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15615

include/rocksdb/arena.h

@@ -1,45 +0,0 @@
-// Copyright (c) 2013, Facebook, Inc.  All rights reserved.
-// This source code is licensed under the BSD-style license found in the
-// LICENSE file in the root directory of this source tree. An additional grant
-// of patent rights can be found in the PATENTS file in the same directory.
-// Copyright (c) 2011 The LevelDB 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 the AUTHORS file for names of contributors.
-//
-// Arena class defines memory allocation methods. It's used by memtable and
-// skiplist.
-
-#ifndef STORAGE_ROCKSDB_INCLUDE_ARENA_H_
-#define STORAGE_ROCKSDB_INCLUDE_ARENA_H_
-
-#include <limits>
-#include <memory>
-
-namespace rocksdb {
-
-class Arena {
- public:
-  Arena() {};
-  virtual ~Arena() {};
-
-  // Return a pointer to a newly allocated memory block of "bytes" bytes.
-  virtual char* Allocate(size_t bytes) = 0;
-
-  // Allocate memory with the normal alignment guarantees provided by malloc.
-  virtual char* AllocateAligned(size_t bytes) = 0;
-
-  // Returns an estimate of the total memory used by arena.
-  virtual const size_t ApproximateMemoryUsage() = 0;
-
-  // Returns the total number of bytes in all blocks allocated so far.
-  virtual const size_t MemoryAllocatedBytes() = 0;
-
- private:
-  // No copying allowed
-  Arena(const Arena&);
-  void operator=(const Arena&);
-};
-
-}  // namespace rocksdb
-
-#endif  // STORAGE_ROCKSDB_INCLUDE_ARENA_H_

include/rocksdb/memtablerep.h

@@ -33,11 +33,9 @@
 // iteration over the entire collection is rare since doing so requires all the
 // keys to be copied into a sorted data structure.
 
-#ifndef STORAGE_ROCKSDB_DB_MEMTABLEREP_H_
-#define STORAGE_ROCKSDB_DB_MEMTABLEREP_H_
+#pragma once
 
 #include <memory>
-#include "rocksdb/slice_transform.h"
 
 namespace rocksdb {
 
@@ -199,5 +197,3 @@ extern MemTableRepFactory* NewHashLinkListRepFactory(
     const SliceTransform* transform, size_t bucket_count = 50000);
 
 }
-
-#endif // STORAGE_ROCKSDB_DB_MEMTABLEREP_H_