Update paint properties on animate motion transform updates

This patch updates SVGAnimateMotionElement so that changes to the
animate motion transform call setNeedsPaintPropertyUpdate. A followup
patch will unify the behavior of the setNeedsTransformUpdate() calls.

With this patch and --enable-blink-features=SlimmingPaintInvalidation,
new tests pass:
  svg/animations/animateMotion-fill-freeze.html
  svg/animations/animateMotion-fill-remove.html
  svg/animations/animateMotion_changingPath.html
+7 more

BUG=645667

Review-Url: https://codereview.chromium.org/2577993003
Cr-Commit-Position: refs/heads/master@{#438915}

third_party/WebKit/Source/core/svg/SVGAnimateMotionElement.cpp

@@ -299,6 +299,10 @@ void SVGAnimateMotionElement::updateAnimationMode() {
 void SVGAnimateMotionElement::invalidateForAnimateMotionTransformChange(
     LayoutObject& object) {
   object.setNeedsTransformUpdate();
+  if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled()) {
+    // The transform paint property relies on the SVG transform value.
+    object.setNeedsPaintPropertyUpdate();
+  }
   markForLayoutAndParentResourceInvalidation(&object);
 }