Marked virtual/softwarecompositing/lots-of-img-layers-with-opacity.html NeedsRebaseline.

BUG=376502
TBR=timvolodine@chromium.org

Review URL: https://codereview.chromium.org/291343003

git-svn-id: svn://svn.chromium.org/blink/trunk@174496 bbb929c8-8fbe-4397-9dbb-9b2b20218538