Go back to old underline position and thickness logic

In r174431 from May this year we changed the underline position and
thickness logic to respect the underline data specified in the font.
While this improved rendering for certain fonts and scripts it did cause
a regression for others. This change reverts to the old behavior while
we figure out how to handle fonts with inaccurate or undesirable
metrics.

BUG=408075
R=scottmg@chromium.org, cpu@chromium.org

Review URL: https://codereview.chromium.org/550163003

git-svn-id: svn://svn.chromium.org/blink/trunk@181591 bbb929c8-8fbe-4397-9dbb-9b2b20218538