[NaCl SDK] Add nacl_mounts to NaCl SDK build. Experimental for now.

native_client_sdk/src/libraries/nacl_mounts/mount_node_mem.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.
  */
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 #ifndef LIBRARIES_NACL_MOUNTS_MOUNT_NODE_MEM_H_
 #define LIBRARIES_NACL_MOUNTS_MOUNT_NODE_MEM_H_
 
 #include "nacl_mounts/mount_node.h"
 
 class MountNodeMem : public MountNode {
  public:
   MountNodeMem(Mount* mount, int ino, int dev);
 
 protected:
   virtual ~MountNodeMem();
   virtual bool Init(int mode, short uid, short gid);
 
 public:
   // Normal read/write operations on a file
   virtual int Read(size_t offs, void* buf, size_t count);
   virtual int Write(size_t offs, const void* buf, size_t count);
   virtual int Truncate(size_t size);
 
  private:
   char* data_;
   size_t capacity_;
   friend class MountMem;
 };
 
 #endif  // LIBRARIES_NACL_MOUNTS_MOUNT_NODE_MEM_H_
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