Fix sharded perf test host forwarder sharing

build/android/pylib/forwarder.py

 # 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.
 
 # pylint: disable=W0212
 
 import fcntl
 import logging
 import os
 import psutil
@@ skipping 231 matching lines @@
   @staticmethod
   def _GetPidForLock():
     """Returns the PID used for host_forwarder initialization.
 
     In case multi-process sharding is used, the PID of the "sharder" is used.
     The "sharder" is the initial process that forks that is the parent process.
     By default, multi-processing is not used. In that case the PID of the
     current process is returned.
     """
     use_multiprocessing = Forwarder._MULTIPROCESSING_ENV_VAR in os.environ
-    return os.getppid() if use_multiprocessing else os.getpid()
+    return os.getpgrp() if use_multiprocessing else os.getpid()
 
   def _InitHostLocked(self):
     """Initializes the host forwarder daemon.
 
     Note that the global lock must be acquired before calling this method. This
     method kills any existing host_forwarder process that could be stale.
     """
     # See if the host_forwarder daemon was already initialized by a concurrent
     # process or thread (in case multi-process sharding is not used).
     pid_for_lock = Forwarder._GetPidForLock()
@@ skipping 77 matching lines @@
     # sure that the old version of device_forwarder (not supporting
     # 'kill-server') is not running on the bots anymore.
     timeout_sec = 5
     try:
       device.KillAll(
           'device_forwarder', blocking=True, timeout=timeout_sec)
     except device_errors.CommandFailedError:
       pids = device.old_interface.ExtractPid('device_forwarder')
       if pids:
         raise