Remove LayoutIndicator which is basically dead code

The LayoutIndicator is being used for one assert which seems excessive.  The
original idea seems to be on hold and the other patches for the parallel layout
effort have been removed as well.

R=eseidel
BUG=289678

Review URL: https://codereview.chromium.org/140733004

git-svn-id: svn://svn.chromium.org/blink/trunk@165258 bbb929c8-8fbe-4397-9dbb-9b2b20218538