Don't discard stderr.

R=maruel@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/14643009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@197419 0039d316-1c4b-4281-b951-d872f2087c98

subprocess2.py

@@ -355,7 +355,6 @@ class Popen(subprocess.Popen):
     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)