The Windows SDK contains some very long paths. When those are added to
the 40-character hash directory and the other path components it is easy
to hit the Windows 260-character MAX_PATH limit. In addition, the 40
character hash makes paths unwieldy in VsChromium search results and
elsewhere.

A ten character hash should be more than enough to avoid collisions - if
we upload a million toolchain packages then there will be about a 50%
chance of a name collision - we won't upload more than a thousand.

This was tested by copying the current toolchain file on Google storage
to a truncated name and then changing to that hash in vs_toolchain.py.
It was also necessary to copy the updates from depot_tools to
third_party\depot_tools. This means that we can't actually start using
short hashes until depot_tools has rolled.

We probably won't use a shorter hash until we next roll the toolchain,
just because changing the toolchain hash is mildly disruptive.

Bug: 1120785
Change-Id: I878b058857cbe9cb72a72b535864404eede33f3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2376030Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>