Use new downcast helper for blink::SVGRadialGradientElement

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

Bug: 891908
Change-Id: I2ae9b50ca2eb0617da5fd2838bf95a991fe00a33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936617Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Abhijeet | Igalia <abhijeet@igalia.com>
Cr-Commit-Position: refs/heads/master@{#720490}

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

@@ -37,7 +37,7 @@ LayoutSVGResourceRadialGradient::~LayoutSVGResourceRadialGradient() = default;
 bool LayoutSVGResourceRadialGradient::CollectGradientAttributes() {
   DCHECK(GetElement());
   attributes_wrapper_->Set(RadialGradientAttributes());
-  return ToSVGRadialGradientElement(GetElement())
+  return To<SVGRadialGradientElement>(GetElement())
       ->CollectGradientAttributes(MutableAttributes());
 }
 

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

@@ -628,7 +628,7 @@ void WriteSVGResourceContainer(WTF::TextStream& ts,
     // gradients using xlink:href, we need to build the full inheritance chain,
     // aka. collectGradientProperties()
     RadialGradientAttributes attributes;
-    ToSVGRadialGradientElement(gradient->GetElement())
+    To<SVGRadialGradientElement>(gradient->GetElement())
         ->CollectGradientAttributes(attributes);
     WriteCommonGradientProperties(ts, attributes);
 

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

@@ -110,7 +110,7 @@ static void SetGradientAttributes(const SVGGradientElement& element,
 
   if (!is_radial)
     return;
-  const SVGRadialGradientElement& radial = ToSVGRadialGradientElement(element);
+  const auto& radial = To<SVGRadialGradientElement>(element);
 
   if (!attributes.HasCx() && radial.cx()->IsSpecified())
     attributes.SetCx(radial.cx()->CurrentValue());
@@ -140,7 +140,7 @@ bool SVGRadialGradientElement::CollectGradientAttributes(
 
   while (true) {
     SetGradientAttributes(*current, attributes,
-                          IsSVGRadialGradientElement(*current));
+                          IsA<SVGRadialGradientElement>(*current));
     visited.insert(current);
 
     current = current->ReferencedElement();