Mojo: Add signal for new data pipe consumer data

mojo/edk/system/data_pipe_consumer_dispatcher.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 MOJO_EDK_SYSTEM_DATA_PIPE_CONSUMER_DISPATCHER_H_
 #define MOJO_EDK_SYSTEM_DATA_PIPE_CONSUMER_DISPATCHER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 99 matching lines @@
   uint32_t two_phase_max_bytes_read_ = 0;
 
   bool in_transit_ = false;
   bool is_closed_ = false;
   bool peer_closed_ = false;
   bool transferred_ = false;
 
   uint32_t read_offset_ = 0;
   uint32_t bytes_available_ = 0;
 
+  // Indicates whether any new data is available since the last read attempt.
+  bool new_data_available_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(DataPipeConsumerDispatcher);
 };
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_DATA_PIPE_CONSUMER_DISPATCHER_H_