Eliminate large chunks of nearly duplicated code for table-row-group border calculation.

calcOuterBorderBefore() and calcOuterBorderAfter() were almost identical.
So were calcOuterBorderStart() and calcOuterBorderEnd().

Merge them into calcBlockDirectionOuterBorder() and calcInlineDirectionOuterBorder().

This is just code cleanup; no behavior changes intended.

BUG=none

Review URL: https://codereview.chromium.org/145603002

git-svn-id: svn://svn.chromium.org/blink/trunk@165746 bbb929c8-8fbe-4397-9dbb-9b2b20218538