Revert "Empty inline elements always get a line box."

This reverts r175205 (commit 897701c1df774bdf053e1329fbd1a038f6eb54f7)
as it is suspected this caused an incorrect cast in RenderBlockFlow.

TBR=inferno@chromium.org,robhogan@gmail.com
BUG=387211

Review URL: https://codereview.chromium.org/348243003

git-svn-id: svn://svn.chromium.org/blink/trunk@176697 bbb929c8-8fbe-4397-9dbb-9b2b20218538