Consolidated checks for the PaintBehaviorRenderingSVGMask flag

Move various (more or less) open-coded checks of the
PaintBehaviorRenderingSVGMask flag to SVGRenderSupport, and call the new
function instead.

BUG=420022

Review URL: https://codereview.chromium.org/625933003

git-svn-id: svn://svn.chromium.org/blink/trunk@183250 bbb929c8-8fbe-4397-9dbb-9b2b20218538