Use new downcast helper for blink::SVGTextPathElement

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

Bug: 891908
Change-Id: Ib6f170541589d0be1f9cf5bcc4583cf8427d9ed9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936626Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Abhijeet | Igalia <abhijeet@igalia.com>
Cr-Commit-Position: refs/heads/master@{#720266}

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

@@ -60,8 +60,7 @@ bool LayoutSVGTextPath::IsChildAllowed(LayoutObject* child,
 }
 
 std::unique_ptr<PathPositionMapper> LayoutSVGTextPath::LayoutPath() const {
-  const SVGTextPathElement& text_path_element =
-      ToSVGTextPathElement(*GetNode());
+  const auto& text_path_element = To<SVGTextPathElement>(*GetNode());
   Element* target_element = SVGURIReference::TargetElementFromIRIString(
       text_path_element.HrefString(),
       text_path_element.TreeScopeForIdResolution());

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

@@ -273,7 +273,7 @@ void SVGTextLayoutEngine::LayoutCharactersInTextBoxes(InlineFlowBox* start) {
         continue;
 
       SVGInlineFlowBox* flow_box = ToSVGInlineFlowBox(child);
-      bool is_text_path = IsSVGTextPathElement(*node);
+      bool is_text_path = IsA<SVGTextPathElement>(*node);
       if (is_text_path)
         BeginTextPathLayout(flow_box);
 

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

@@ -36,7 +36,8 @@ LayoutObject* SVGTSpanElement::CreateLayoutObject(const ComputedStyle&,
 bool SVGTSpanElement::LayoutObjectIsNeeded(const ComputedStyle& style) const {
   if (parentNode() &&
       (IsSVGAElement(*parentNode()) || IsSVGTextElement(*parentNode()) ||
-       IsSVGTextPathElement(*parentNode()) || IsSVGTSpanElement(*parentNode())))
+       IsA<SVGTextPathElement>(*parentNode()) ||
+       IsSVGTSpanElement(*parentNode())))
     return SVGElement::LayoutObjectIsNeeded(style);
 
   return false;