Unreviewed gardening on test expectations

Ongoing scrollbar work is two sided, and will need manual rebaselining after the second side lands.

TBR=wjmaclean@chromium.org
BUG=338794

Review URL: https://codereview.chromium.org/140663009

git-svn-id: svn://svn.chromium.org/blink/trunk@166030 bbb929c8-8fbe-4397-9dbb-9b2b20218538