Synchronize attribute before animation ends

After https://codereview.chromium.org/26390004, width and height on
SVGSVGElement are presentation attributes. When they are animated,
they must be synchronized to the attribute system so that the
presentation attribute code can rebuild the corresponding style.

Prior to this patch, the last synchronization (back to base value or
to fill value) never happened because the synchronization happened
after the animation had ended. No animation means no synchronization.
This patch adds a final synchronization before the animation ends so
that the final value is properly synchronized.

BUG=308992,364807

Review URL: https://codereview.chromium.org/248503004

git-svn-id: svn://svn.chromium.org/blink/trunk@172353 bbb929c8-8fbe-4397-9dbb-9b2b20218538