Windows bots are having trouble calling download_from_google_storage.py from the
DEPS hooks.  This should allow it to be called as just "download_from_google_storage".

BUG=
R=maruel@chromium.org

Review URL: https://codereview.chromium.org/15395002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@200939 0039d316-1c4b-4281-b951-d872f2087c98