Example error during "git cl upload":
Traceback (most recent call last):
  File "C:\Google\depot_tools\presubmit_support.py", line 220, in CallCommand
    returncode, stdout = self._RunWithTimeout(cmd, test.stdin, test.kwargs)
  File "C:\Google\depot_tools\presubmit_support.py", line 204, in _RunWithTimeout
    p = subprocess.Popen(cmd, **kwargs)
  File "C:\Google\depot_tools\subprocess2.py", line 143, in __init__
    super(Popen, self).__init__(args, **kwargs)
  File "C:\Google\depot_tools\bootstrap-3_8_0b1_chromium_1_bin\python\bin\Lib\subprocess.py", line 390, in __init__
    errread, errwrite)
  File "C:\Google\depot_tools\bootstrap-3_8_0b1_chromium_1_bin\python\bin\Lib\subprocess.py", line 640, in _execute_child
    startupinfo)
TypeError: environment can only contain strings

Bug: 984182
Change-Id: Id996d73a80845aaeaa061107ed123627091cb600
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1815872
Commit-Queue: Raul Tambre <raul@tambre.ee>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Raul Tambre <raul@tambre.ee>