Bug 1450250: Preserve the behavior of GetOuterSVGElement so that it works for <animate>. r=heycam

It's used by SVGAnimationElement, and otherwise it can't find the root element
if it's under a <use> element.

It also feels like the right thing to do, and didn't break any XBL+svg tests
(though we may as well get rid of those at this point).

Differential Revision: https://phabricator.services.mozilla.com/D2195

MozReview-Commit-ID: Jx1JrTld8EL

dom/svg/SVGContentUtils.cpp

@@ -41,13 +41,13 @@ using namespace mozilla::gfx;
 SVGSVGElement*
 SVGContentUtils::GetOuterSVGElement(nsSVGElement *aSVGElement)
 {
-  nsIContent *element = nullptr;
-  nsIContent *ancestor = aSVGElement->GetFlattenedTreeParent();
+  Element* element = nullptr;
+  Element* ancestor = aSVGElement->GetParentElementCrossingShadowRoot();
 
   while (ancestor && ancestor->IsSVGElement() &&
                      !ancestor->IsSVGElement(nsGkAtoms::foreignObject)) {
     element = ancestor;
-    ancestor = element->GetFlattenedTreeParent();
+    ancestor = element->GetParentElementCrossingShadowRoot();
   }
 
   if (element && element->IsSVGElement(nsGkAtoms::svg)) {