Use new downcast helper for blink::HTMLProgressElement

This CL has goal to use IsA<HTMLProgressElement>(element) in place of
IsHTMLProgressElement(element)

Bug: 891908
Change-Id: Ic141eeff5bddfe0bc897f969e3be3884b0dcd137
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1930543
Commit-Queue: Abhijeet | Igalia <abhijeet@igalia.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718994}

third_party/blink/renderer/core/layout/layout_progress.cc

@@ -35,7 +35,7 @@ LayoutProgress::LayoutProgress(Element* element)
           element->GetDocument().GetTaskRunner(TaskType::kInternalDefault),
           this,
           &LayoutProgress::AnimationTimerFired) {
-  DCHECK(IsHTMLProgressElement(element));
+  DCHECK(IsA<HTMLProgressElement>(element));
 }
 
 LayoutProgress::~LayoutProgress() = default;