Follow-up from this CL: https://chromium-review.googlesource.com/c/chromium/src/+/1036232

Element::VisibleBoundsInVisualViewport() was modified and there was a browser test added to verify the overall integrity of the change, but the method itself could used unit tests as described by pdr@:
https://chromium-review.googlesource.com/c/chromium/src/+/1036232/9/third_party/blink/renderer/core/dom/element.cc#1282