Fix text-overflow:ellipsis.

This regressed in 3db9471ae80bd492f2a346113d2323ba8eee0c09.

Accidentally sent some code down the override by sending the
top LayoutUnit instead of the left/right LayoutUnit. The
root problem was bad overloading, which is also fixed in
this patch. Inlined the overloaded method since one of
the calls was only called from one place.

The new test demonstrates the ellipsizing, but that doesn't
show through in the render tree dump. We don't get real
test coverage here until we either start doing pixel tests
or start exposing ellipsis in the render tree dumps.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/751483002