Rebaseline virtual/threaded/compositing/visibility/visibility-image-layers.html

The image result changed on Win, probably due to:
Chromium r283229 "content: Enable impl-side painting on Windows"
https://codereview.chromium.org/392623003/

The visual change is imperceivable so I'll rebaseline.

BUG=169282
TBR=reveman

Review URL: https://codereview.chromium.org/396833005

git-svn-id: svn://svn.chromium.org/blink/trunk@178229 bbb929c8-8fbe-4397-9dbb-9b2b20218538