Workaround for renderer glitch.

Table renderer ocassionally renders zero-width cells over right border of
perceding cells. This may appear when user hovers cell, or something like that.

If we replace right borders with left borders, then glitch doesn't appear.

BUG=264663

Review URL: https://chromiumcodereview.appspot.com/21087010

git-svn-id: svn://svn.chromium.org/blink/trunk@156779 bbb929c8-8fbe-4397-9dbb-9b2b20218538