Rename some table headings in LayoutTest results.html

It's confusing to have a column labelled "expected failure" that usually
contains the word "pass". I've trimmed these columns to just be labeled
"actual" and "expected".

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/48213003

git-svn-id: svn://svn.chromium.org/blink/trunk@160996 bbb929c8-8fbe-4397-9dbb-9b2b20218538