[SVG] animateMotion is freezing at the end by default

Need to mark the renderer for layout after doing a reset of the transform at the end of the animation.
Otherwise transform will not be applied.

R=pdr@chromium.org, schenney@chromium.org, dschulze@chromium.org, fmalita@chromium.org
BUG=265835

Review URL: https://chromiumcodereview.appspot.com/21262002

git-svn-id: svn://svn.chromium.org/blink/trunk@155209 bbb929c8-8fbe-4397-9dbb-9b2b20218538