Add a fake requestAnimationFrame to SVGImage

This CL adds a fake implementation of requestAnimationFrame to SVGImage so that
when we move layout to be driven off of requestAnimationFrame we'll actually
layout SVGImages.

BUG=340357

Review URL: https://codereview.chromium.org/142443005

git-svn-id: svn://svn.chromium.org/blink/trunk@166353 bbb929c8-8fbe-4397-9dbb-9b2b20218538