Remove unnecessary repaint in SVGSVGElement::updateCurrentTranslate

This patch removes an unnecessary repaint of the dirty tree in
SVGSVGElement::updateCurrentTranslate.

Review URL: https://codereview.chromium.org/268863005

git-svn-id: svn://svn.chromium.org/blink/trunk@173274 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Store SVGElement instead of SVGElementInstance for instancesForElement

BUG=313438

Review URL: https://codereview.chromium.org/266063002

git-svn-id: svn://svn.chromium.org/blink/trunk@173275 bbb929c8-8fbe-4397-9dbb-9b2b20218538