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

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

 // 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.
 
 #include "nacl_io/devfs/tty_event_emitter.h"
 
 #include <algorithm>
 
 namespace nacl_io {
 
 TtyEventEmitter::TtyEventEmitter(size_t size)
     : fifo_(std::max<size_t>(1, size)) {
   UpdateStatus_Locked();
 }
 
-size_t TtyEventEmitter::Read_Locked(char* data, size_t len) {
-  size_t out_len = fifo_.Read(data, len);
+Error TtyEventEmitter::Read_Locked(char* data, size_t len, int* out_bytes) {
+  *out_bytes = fifo_.Read(data, len);
 
   UpdateStatus_Locked();
-  return out_len;
+  return 0;
 }
 
-size_t TtyEventEmitter::Write_Locked(const char* data, size_t len) {
-  size_t out_len = fifo_.Write(data, len);
+Error TtyEventEmitter::Write_Locked(const char* data, size_t len,
+                                    int* out_bytes) {
+  *out_bytes = fifo_.Write(data, len);
 
   UpdateStatus_Locked();
-  return out_len;
+  return 0;
 }
 
 }  // namespace nacl_io