The code in _downloader_worker_thread() does not work with Python 3:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.7/threading.py", line 926, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.7/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/home/rakuco/src/depot_tools/download_from_google_storage.py", line 343, in _downloader_worker_thread
    elif re.search(r'executable:\s*1', out):
  File "/usr/lib/python3.7/re.py", line 183, in search
    return _compile(pattern, flags).search(string)
TypeError: cannot use a string pattern on a bytes-like object

Bug: 984182, 1007872
Change-Id: I09df8169d802b010596ac4f34501b4bda805e6f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1844833
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>