Add FIXME to RenderBlockFlow::checkLinesForTextOverflow

Add FIXME for hard-coded text direction for ellipsis in RenderBlockFlow
::checkLinesForTextOverflow. While the direction likely doesn't matter
for the metrics that might change for some locals.

BUG=333004
R=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/148703002

git-svn-id: svn://svn.chromium.org/blink/trunk@165913 bbb929c8-8fbe-4397-9dbb-9b2b20218538