Use new downcast helper for blink::SVGEllipseElement

This CL has goal to use IsA<SVGEllipseElement>(element) in place of
IsSVGEllipseElement(element)

Bug: 891908
Change-Id: I94acafea6e7b5fbf87731859474c9915070a7407
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936573Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Abhijeet | Igalia <abhijeet@igalia.com>
Cr-Commit-Position: refs/heads/master@{#720418}

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

@@ -360,7 +360,7 @@ static WTF::TextStream& operator<<(WTF::TextStream& ts,
                        element->x2()->CurrentValue()->Value(length_context));
     WriteNameValuePair(ts, "y2",
                        element->y2()->CurrentValue()->Value(length_context));
-  } else if (IsSVGEllipseElement(*svg_element)) {
+  } else if (IsA<SVGEllipseElement>(*svg_element)) {
     WriteNameValuePair(ts, "cx",
                        length_context.ValueForLength(svg_style.Cx(), style,
                                                      SVGLengthMode::kWidth));

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

@@ -48,7 +48,7 @@ bool TargetCanHaveMotionTransform(const SVGElement& target) {
          IsA<SVGUseElement>(target) || IsSVGImageElement(target) ||
          IsSVGSwitchElement(target) || IsSVGPathElement(target) ||
          IsA<SVGRectElement>(target) || IsSVGCircleElement(target) ||
-         IsSVGEllipseElement(target) || IsA<SVGLineElement>(target) ||
+         IsA<SVGEllipseElement>(target) || IsA<SVGLineElement>(target) ||
          IsA<SVGPolylineElement>(target) || IsA<SVGPolygonElement>(target) ||
          IsA<SVGTextElement>(target) || IsSVGClipPathElement(target) ||
          IsSVGMaskElement(target) || IsSVGAElement(target) ||

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

@@ -498,7 +498,7 @@ LayoutObject* SVGUseElement::CreateLayoutObject(const ComputedStyle& style,
 
 static bool IsDirectReference(const SVGElement& element) {
   return IsSVGPathElement(element) || IsA<SVGRectElement>(element) ||
-         IsSVGCircleElement(element) || IsSVGEllipseElement(element) ||
+         IsSVGCircleElement(element) || IsA<SVGEllipseElement>(element) ||
          IsA<SVGPolygonElement>(element) || IsA<SVGPolylineElement>(element) ||
          IsA<SVGTextElement>(element);
 }