[NaCl SDK] nacl_io: Add flow control the JavaScript pipes.

native_client_sdk/src/libraries/nacl_io/devfs/tty_event_emitter.h

 // Copyright 2013 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_DEVFS_TTY_EVENT_EMITTER_H_
 #define LIBRARIES_NACL_IO_DEVFS_TTY_EVENT_EMITTER_H_
 
 #include <poll.h>
 #include <stdint.h>
 #include <stdlib.h>
 
 #include "nacl_io/fifo_char.h"
 #include "nacl_io/fifo_null.h"
 #include "nacl_io/stream/stream_event_emitter.h"
 
 #include "sdk_util/auto_lock.h"
 #include "sdk_util/macros.h"
 
 namespace nacl_io {
 
 class TtyEventEmitter;
 typedef sdk_util::ScopedRef<TtyEventEmitter> ScopedTtyEventEmitter;
 
 class TtyEventEmitter : public StreamEventEmitter {
  public:
   explicit TtyEventEmitter(size_t size);
 
-  size_t Read_Locked(char* data, size_t len);
-  size_t Write_Locked(const char* data, size_t len);
+  Error Read_Locked(char* data, size_t len, int* out_bytes);
+  Error Write_Locked(const char* data, size_t len, int* out_bytes);
 
  protected:
   virtual FIFOChar* in_fifo() { return &fifo_; }
   virtual FIFONull* out_fifo() { return &null_; }
 
  private:
   FIFOChar fifo_;
   FIFONull null_;
   DISALLOW_COPY_AND_ASSIGN(TtyEventEmitter);
 };
 
 }  // namespace nacl_io
 
 #endif  // LIBRARIES_NACL_IO_DEVFS_TTY_EVENT_EMITTER_H_