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/+/1936573
Reviewed-by: Kentaro Hara <[email protected]>
Commit-Queue: Abhijeet | Igalia <[email protected]>
Cr-Commit-Position: refs/heads/master@{#720418}
3 files changed