Add treehash tool for win_toolchain

Add treehash tool for win_toolchain

This matches what the python does in get_toolchain_if_necessary.py
and produces the same SHA1. This allows the toolchain "up-to-date"
check to be much faster (from ~1.1s -> ~0.1s on Z620). Since this is
run in the hot path of GN generation we don't want it to be slow.
See linked bug for timing details.

This is intended to replace a bunch of code in the above python script
but I'll do the integration as a separate change.

R=brettw@chromium.org, dpranke@chromium.org
BUG=360878

[Dirk Pranke, 2014-04-08 19:07:08]

Why is this run during GN generation?

[scottmg, 2014-04-08 19:36:33]

I have no idea! That'll teach me to write code late at night after
sheriffing.

(Mostly just because the toolchain "update" and "get_location" are rolled
into one script. I'll figure out how to split them apart instead.)


On Tue, Apr 8, 2014 at 12:07 PM, <dpranke@chromium.org> wrote:

> Why is this run during GN generation?
>
> https://codereview.chromium.org/228093002/
>

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[scottmg, 2014-04-08 20:01:04]

Closing in preference to https://codereview.chromium.org/226643011/.

[brettw, 2014-04-08 20:23:38]

On 2014/04/08 19:07:08, Dirk Pranke wrote:
> Why is this run during GN generation?

I'm glad somebody is paying attention!