Update comments in the Native Messaging example

chrome/common/extensions/docs/examples/api/nativeMessaging/host/native-messaging-example-host

 #!/usr/bin/env python
 # 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.
 
 # A simple native messaging host. Shows a Tkinter dialog with incoming messages
 # that also allows to send message back to the webapp.
 
 import struct
 import sys
@@ skipping 11 matching lines @@
    # Write message size.
   sys.stdout.write(struct.pack('I', len(message)))
   # Write the message itself.
   sys.stdout.write(message)
   sys.stdout.flush()
 
 # Thread that reads messages from the webapp.
 def read_thread_func(queue):
   message_number = 0
   while 1:
-    # Read the message type (first 4 bytes).
+    # Read the message length (first 4 bytes).
     text_length_bytes = sys.stdin.read(4)
 
     if len(text_length_bytes) == 0:
       if queue:
         queue.put(None)
       sys.exit(0)
 
-    # Read the message length (4 bytes).
+    # Unpack message length as 4 byte integer.
     text_length = struct.unpack('i', text_length_bytes)[0]
 
     # Read the text (JSON object) of the message.
     text = sys.stdin.read(text_length).decode('utf-8')
 
     if queue:
       queue.put(text)
     else:
       # In headless mode just send an echo message back.
       send_message('{"echo": %s}' % text)
@@ skipping 61 matching lines @@
   thread.daemon = True
   thread.start()
 
   main_window.mainloop()
 
   sys.exit(0)
 
 
 if __name__ == '__main__':
   Main()