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

native_client_sdk/src/libraries/nacl_io/fifo_char.h

 // Copyright (c) 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_FIFO_CHAR_H_
 #define LIBRARIES_NACL_IO_FIFO_CHAR_H_
 
 #include <vector>
 
 #include "nacl_io/fifo_interface.h"
 
 #include "sdk_util/macros.h"
 
 namespace nacl_io {
 
 // FIFOChar
 //
 // A FIFOChar is a circular buffer, signalling FULL and EMPTY as appropriate.
 class FIFOChar : public FIFOInterface {
  public:
   explicit FIFOChar(size_t size);
   virtual ~FIFOChar();
 
   virtual bool IsEmpty();
   virtual bool IsFull();
   virtual bool Resize(size_t len);
 
-  size_t ReadAvailable();
-  size_t WriteAvailable();
+  virtual size_t ReadAvailable();
+  virtual size_t WriteAvailable();
 
   // Reads out no more than the requested len without updating the tail.
   // Returns actual amount read.
   size_t Peek(void* buf, size_t len);
 
   // Reads out the data making room in the FIFO.  Returns actual amount
   // read.
   size_t Read(void* buf, size_t len);
 
   // Writes into the FIFO no more than len bytes, returns actual amount
   // written.
   size_t Write(const void* buf, size_t len);
 
 private:
   char* buffer_;
   size_t size_;   // Size of the FIFO
   size_t avail_;  // How much data is currently available
   size_t tail_;   // Next read location
 
   DISALLOW_COPY_AND_ASSIGN(FIFOChar);
 };
 
 }  // namespace nacl_io
 
 #endif  // LIBRARIES_NACL_IO_FIFO_CHAR_H_