Currently on Chrome OS we use 1 dip separators in menus. Is this desired?
For Windows we use 1px. Is this correct? If not, we should change to 1 dip, like Chrome OS (possibly even the same implementation). If not, we still need to worry about the gaps that appear between the button highlights and the separators. These gaps appear because the 1px line is drawn in the middle of the 1dip that is reserved, so e.g. at 300% there's  a 1px gap on each side of the line.

see https://codereview.chromium.org/2813703003/ and particularly comment 24 for discussion.