Don't discard stderr.

subprocess2.py

 # coding=utf8
 # 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.
 """Collection of subprocess wrapper functions.
 
 In theory you shouldn't need anything else in subprocess, or this module failed.
 """
 
 import cStringIO
@@ skipping 337 matching lines @@
     # When the pipe fills up, it would deadlock this process.
     if self.stdout and not self.stdout_cb and not self.stdout_is_void:
       stdout = []
       self.stdout_cb = stdout.append
     if self.stderr and not self.stderr_cb and not self.stderr_is_void:
       stderr = []
       self.stderr_cb = stderr.append
     self._tee_threads(input)
     if stdout is not None:
       stdout = ''.join(stdout)
-    stderr = None
     if stderr is not None:
       stderr = ''.join(stderr)
     return (stdout, stderr)
 
 
 def communicate(args, timeout=None, **kwargs):
   """Wraps subprocess.Popen().communicate() and add timeout support.
 
   Returns ((stdout, stderr), returncode).
 
@@ skipping 71 matching lines @@
 
   - Throws if return code is not 0.
   - Works even prior to python 2.7.
   - Blocks stdin by default if not specified since no output will be visible.
   - As per doc, "The stdout argument is not allowed as it is used internally."
   """
   kwargs.setdefault('stdin', VOID)
   if 'stdout' in kwargs:
     raise ValueError('stdout argument not allowed, it will be overridden.')
   return check_call_out(args, stdout=PIPE, **kwargs)[0]