Remove SVGPaintType enum hardcoding

We do not have to follow the specified values for SVG2 anymore, so use the default ordering.
Later on this could help since the enum could potentially be bitpacked to less bits.

Review URL: https://codereview.chromium.org/205863002

git-svn-id: svn://svn.chromium.org/blink/trunk@169695 bbb929c8-8fbe-4397-9dbb-9b2b20218538