[NaCl SDK] nacl_io: big refactor to return error value (errno).

native_client_sdk/src/libraries/nacl_io/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.
  */
 #ifndef LIBRARIES_NACL_IO_MOUNT_NODE_MEM_H_
 #define LIBRARIES_NACL_IO_MOUNT_NODE_MEM_H_
 
 #include "nacl_io/mount_node.h"
 
 class MountNodeMem : public MountNode {
  public:
   explicit MountNodeMem(Mount* mount);
 
  protected:
   virtual ~MountNodeMem();
 
  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 FTruncate(off_t size);
+  virtual Error Read(size_t offs, void* buf, size_t count, int* out_bytes);
+  virtual Error Write(size_t offs,
+                      const void* buf,
+                      size_t count,
+                      int* out_bytes);
+  virtual Error FTruncate(off_t size);
 
  private:
   char* data_;
   size_t capacity_;
   friend class MountMem;
 };
 
 #endif  // LIBRARIES_NACL_IO_MOUNT_NODE_MEM_H_