Kill outlineBox

The outline box concept wasn't clearly defined. It was also unneeded
if we track the outline into the visual overflow, which we now do!

This change is a mechanical removal of the associated code. It keeps
the logic in repaintAfterLayout that handles changes in visual overflow
as it is required to correctly invalidate some cases where our
simplistic visual overflow model using a single rect falls short.

Most tests changes correspond to less invalidation, except for
* fast/repaint/4776765.html which is getting 2 new invalidations
  coresponding to getting a 5px outline.
* fast/box-shadow/negative-shadow-box*.html which grew to include
  the full box-shadow instead of being the box's size.

BUG=345452

Review URL: https://codereview.chromium.org/210043008

git-svn-id: svn://svn.chromium.org/blink/trunk@170115 bbb929c8-8fbe-4397-9dbb-9b2b20218538