Mark software compositing tests as rebaseline needed.

These were changed by http://crrev.com/219763

BUG=280213
R=jianli@chromium.org

Review URL: https://codereview.chromium.org/23597004

git-svn-id: svn://svn.chromium.org/blink/trunk@156792 bbb929c8-8fbe-4397-9dbb-9b2b20218538