Add UseCounter for SVGPoint.matrixTransform.

Requested by https://www.w3.org/Graphics/SVG/WG/track/actions/3534.

R=pdr,krit
BUG=

Review URL: https://codereview.chromium.org/104023003

git-svn-id: svn://svn.chromium.org/blink/trunk@163164 bbb929c8-8fbe-4397-9dbb-9b2b20218538