Fold SVGRenderSupport::fillOrStrokePath into only user

Only used in SVGTextRunRenderingContext::drawSVGGlyphs. Fold up and
simplify. Clean up some includes.

BUG=420022

Review URL: https://codereview.chromium.org/657553002

git-svn-id: svn://svn.chromium.org/blink/trunk@183732 bbb929c8-8fbe-4397-9dbb-9b2b20218538