nrwt: broken for chromium on vista

nrwt: broken for chromium on vista
https://bugs.webkit.org/show_bug.cgi?id=89988

Reviewed by Tony Chang.

r121194 removed support for 'chromium-win-vista' as a separate
port, but this actually prevented the code from running on vista
at all, which is unduly harsh and broke the websocket tests on
the (non-webkit) chromium bots that are still running on vista.

It's probably good enough to pretend that vista is win7 instead;
some layout tests will still fail but at least things'll run.

* Scripts/webkitpy/layout_tests/port/chromium_win.py:
(ChromiumWinPort.determine_full_port_name):
* Scripts/webkitpy/layout_tests/port/chromium_win_unittest.py:
(ChromiumWinTest.test_versions):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121266 268f45cc-cd09-0410-ab3c-d52691b4dbfc