Add UseCounters for the reflected SVGElement.xml* attributes

Erik Dahlström <ed@opera.com> is going to propose dropping these:
https://www.w3.org/Graphics/SVG/WG/wiki/Proposals/dropxmlattributes

BUG=341854
NOTRY=true

Review URL: https://codereview.chromium.org/889533004

git-svn-id: svn://svn.chromium.org/blink/trunk@189278 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed