Use new downcast helper for blink::SVGClipPathElement

This CL has two goals,
  1. Use To<SVGClipPathElement> as new downcast helper
  2. Use IsA<SVGClipPathElement>(element) in place of
     IsSVGClipPathElement(element)

Bug: 891908
Change-Id: Ic2972f94fc26db68a5beca96d9ec23ca2ecb218b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936571
Commit-Queue: Abhijeet | Igalia <abhijeet@igalia.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720504}

third_party/blink/renderer/core/layout/svg/layout_svg_resource_clipper.cc

@@ -217,7 +217,7 @@ void LayoutSVGResourceClipper::CalculateLocalClipBounds() {
 }
 
 SVGUnitTypes::SVGUnitType LayoutSVGResourceClipper::ClipPathUnits() const {
-  return ToSVGClipPathElement(GetElement())
+  return To<SVGClipPathElement>(GetElement())
       ->clipPathUnits()
       ->CurrentValue()
       ->EnumValue();
@@ -226,7 +226,7 @@ SVGUnitTypes::SVGUnitType LayoutSVGResourceClipper::ClipPathUnits() const {
 AffineTransform LayoutSVGResourceClipper::CalculateClipTransform(
     const FloatRect& reference_box) const {
   AffineTransform transform =
-      ToSVGClipPathElement(GetElement())
+      To<SVGClipPathElement>(GetElement())
           ->CalculateTransform(SVGElement::kIncludeMotionTransform);
   if (ClipPathUnits() == SVGUnitTypes::kSvgUnitTypeObjectboundingbox) {
     transform.Translate(reference_box.X(), reference_box.Y());

third_party/blink/renderer/core/svg/svg_animate_motion_element.cc

@@ -50,7 +50,7 @@ bool TargetCanHaveMotionTransform(const SVGElement& target) {
          IsA<SVGRectElement>(target) || IsSVGCircleElement(target) ||
          IsA<SVGEllipseElement>(target) || IsA<SVGLineElement>(target) ||
          IsA<SVGPolylineElement>(target) || IsA<SVGPolygonElement>(target) ||
-         IsA<SVGTextElement>(target) || IsSVGClipPathElement(target) ||
+         IsA<SVGTextElement>(target) || IsA<SVGClipPathElement>(target) ||
          IsA<SVGMaskElement>(target) || IsSVGAElement(target) ||
          IsSVGForeignObjectElement(target);
 }