Ensure/document that the first parameter to the native messaging host is the origin

chrome/test/data/native_messaging/native_hosts/echo.py

 #!/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 client in python.
 # All this client does is echo the text it receives back at the extension.
 
 import os
 import platform
 import sys
 import struct
 
 def WriteMessage(message):
   try:
     sys.stdout.write(struct.pack("I", len(message)))
     sys.stdout.write(message)
     sys.stdout.flush()
     return True
   except IOError:
     return False
 
 def Main():
   message_number = 0
 
-  caller_url = None
   parent_window = None
 
   if len(sys.argv) < 2:
     sys.stderr.write("URL of the calling application is not specified.\n")
     return 1
+  caller_url = sys.argv[1]
+
   # TODO(sergeyu): Use argparse module to parse the arguments (not available in
   # Python 2.6).
-  for arg in sys.argv[1:]:
+  for arg in sys.argv[2:]:
     if arg.startswith('--'):
       if arg.startswith('--parent-window='):
         parent_window = long(arg[len('--parent-window='):])
-    elif caller_url == None:
-      caller_url = arg
 
   # Verify that the process was started in the correct directory.
   cwd = os.getcwd()
   script_path = os.path.dirname(os.path.abspath(sys.argv[0]))
   if cwd.lower() != script_path.lower():
     sys.stderr.write('Native messaging host started in a wrong directory.')
     return 1
 
   # Verify that --parent-window parameter is correct.
   if platform.system() == 'Windows' and parent_window:
@@ skipping 35 matching lines @@
 
     message_number += 1
 
     message = '{{"id": {0}, "echo": {1}, "caller_url": "{2}"}}'.format(
           message_number, text, caller_url).encode('utf-8')
     if not WriteMessage(message):
       break
 
 if __name__ == '__main__':
   sys.exit(Main())