This is a reland of 5d284fdf

Always convert the input to bytes and write to sys.stdout (in Python2)
and sys.stdout.buffer (in Python 3).

Original change's description:
> gclient_utils: buffer output as bytestrings in Annotated
>
> In Python 3 byestrings and normal strings can't be concatenated.
> To fix this we buffer as bytestrings in the Annotated wrapper.
> We can't decode to a string because the output might come byte-by-byte, so it doesn't work with Unicode characters like ✔.
>
> Also had to update gclient_test.py, where double-wrapping stdout with Annotated caused made output not work and include_zero=True working caused other unintended side-effects.
>
> Example error from "fetch chromium":
> Traceback (most recent call last):
>   File "C:\Google\depot_tools\gclient_scm.py", line 1045, in _Clone
>     self._Run(clone_cmd, options, cwd=self._root_dir, retry=True,
>   File "C:\Google\depot_tools\gclient_scm.py", line 1370, in _Run
>     gclient_utils.CheckCallAndFilter(cmd, env=env, **kwargs)
>   File "C:\Google\depot_tools\gclient_utils.py", line 583, in CheckCallAndFilter
>     show_header_if_necessary(needs_header, attempt)
>   File "C:\Google\depot_tools\gclient_utils.py", line 533, in show_header_if_necessary
>     stdout_write(header.encode())
>   File "C:\Google\depot_tools\gclient_utils.py", line 391, in write
>     obj[0] += out
> TypeError: can only concatenate str (not "bytes") to str
>
> Bug: 984182
> Change-Id: If7037d30e9faf524f2405258281f6e6cd0bcdcae
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1778745
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
> Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
> Auto-Submit: Raul Tambre <raul@tambre.ee>

Bug: 984182
Change-Id: Ifafb5e16a517c4c38dd4c9d5c6d4c3f994838bc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1845504Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>