SVGInlineTextBox run bounds should compensate for ascent.

The current TextRunPaintInfo bounds for SVG text are off vertically by
the font ascent (fragments are positioned on the baseline, and we use
their position as the box origin).

We need to adjust the bounds position to compensate for ascent,
similarly to SVGInlineTextBox::calculateBoundaries() and
RenderSVGInlineText::positionForPoint().

There are no observable side effects at this time, but the incorrect
text run bounds are causing problems when text blob quickreject is
enabled (or possibly text region tracking in the future).

BUG=408807
R=pdr@chromium.org,fs@opera.com,schenney@chromium.org

Review URL: https://codereview.chromium.org/524563003

git-svn-id: svn://svn.chromium.org/blink/trunk@181101 bbb929c8-8fbe-4397-9dbb-9b2b20218538