[android] Improve reverse forwarder error handling

build/android/adb_reverse_forwarder.py

 #!/usr/bin/env python
 #
 # 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.
 
 """Command line tool for forwarding ports from a device to the host.
 
 Allows an Android device to connect to services running on the host machine,
 i.e., "adb forward" in reverse. Requires |host_forwarder| and |device_forwarder|
@@ skipping 44 matching lines @@
 
   adb = android_commands.AndroidCommands(options.device)
   tool = CreateTool(None, adb)
   forwarder_instance = forwarder.Forwarder(adb, options.build_type)
   try:
     forwarder_instance.Run(port_pairs, tool, options.host)
     while True:
       time.sleep(60)
   except KeyboardInterrupt:
     sys.exit(0)
+  except OSError as e:
+    if e.errno == 2:
+      print 'Unable to start. Make sure you have built host_forwarder.'

[bulach, 2013/03/08 15:15:33]

maybe push this down to forwarder.py Run itself?

+      sys.exit(1)
+    else: raise
   finally:
     forwarder_instance.Close()
 
 
 if __name__ == '__main__':
   main(sys.argv)