[S.P.] Move mask painting to SVGMaskPainter.

BUG=462077

Review URL: https://codereview.chromium.org/967543002

git-svn-id: svn://svn.chromium.org/blink/trunk@191196 bbb929c8-8fbe-4397-9dbb-9b2b20218538
7 files changed