Use new downcast helper for blink::HTMLBRElement

This CL has goal to use To<HTMLBRElement> as new downcast helper

Bug: 891908
Change-Id: Id23a072816c168c77285f635b7928fcc76c0609c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1930762Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Abhijeet | Igalia <abhijeet@igalia.com>
Cr-Commit-Position: refs/heads/master@{#719020}

third_party/blink/renderer/core/editing/commands/replace_selection_command.cc

@@ -2077,7 +2077,7 @@ bool ReplaceSelectionCommand::PerformTrivialReplace(
   if (node_after_insertion_pos && node_after_insertion_pos->parentNode() &&
       IsA<HTMLBRElement>(*node_after_insertion_pos) &&
       ShouldRemoveEndBR(
-          ToHTMLBRElement(node_after_insertion_pos),
+          To<HTMLBRElement>(node_after_insertion_pos),
           VisiblePosition::BeforeNode(*node_after_insertion_pos))) {
     RemoveNodeAndPruneAncestors(node_after_insertion_pos, editing_state);
     if (editing_state->IsAborted())