Disable BitmapImageTests on Windows

They always fail on the WebKit XP (deps) bots. Disabling them, at least temporarily,
to see if the failures might move to other tests.

BUG=327104
TBR=wangxianzhu@chromium.org

Review URL: https://codereview.chromium.org/111443003

git-svn-id: svn://svn.chromium.org/blink/trunk@163555 bbb929c8-8fbe-4397-9dbb-9b2b20218538