Refine expectations for svg/overflow/overflow-on-outermost-svg-element-in-xhtml-defaults.xhtml

BUG=428189
TBR=bokan@chromium.org

Review URL: https://codereview.chromium.org/687153003

git-svn-id: svn://svn.chromium.org/blink/trunk@184576 bbb929c8-8fbe-4397-9dbb-9b2b20218538