Auto-updating script for Windows toolchain

Updates third_party/win_toolchain to pull down a toolchain
based on SHA1. The intention is that this will be a DEPS hook
once it's ready for more broad usage and the rest of
infrastructure is ready.

R=maruel@chromium.org
TBR=cpu@chromium.org
BUG=323300

Review URL: https://codereview.chromium.org/70493006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237369 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed