Adding use counters for CanvasRenderingContext2D.webkitImageSmoothingEnabled

Counting prefixed vs unprefixed.

BUG=341561
R=senorblanco@chromium.org

Review URL: https://codereview.chromium.org/152893005

git-svn-id: svn://svn.chromium.org/blink/trunk@166650 bbb929c8-8fbe-4397-9dbb-9b2b20218538