Test: Don't add scrollbar width to intrinsic width of fixed-width grid items

The scroll bar width should only be added if the width of the grid item is
not fixed.

This test coverage has been inspired from the webkit patch for flexboxes at
https://bugs.webkit.org/attachment.cgi?id=182187&action=diff 

BUG=395788

Review URL: https://codereview.chromium.org/532203002

git-svn-id: svn://svn.chromium.org/blink/trunk@181590 bbb929c8-8fbe-4397-9dbb-9b2b20218538
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