Mark css3/compositing/background-blend-mode-crossfade-image-gradient.html as NeedsManualRebaseline

TBR=enne
BUG=251960

Review URL: https://codereview.chromium.org/261793003

git-svn-id: svn://svn.chromium.org/blink/trunk@173424 bbb929c8-8fbe-4397-9dbb-9b2b20218538