IntersectionObserver -- properly handle "unknown" occlusion state
If we most recently reported a target as "guaranteed visible", then in
the interest of avoiding false positives we must transition to "not
guaranteed visible" if the frame occlusion state becomes "unknown".
This CL also makes a child frame inherit its parent's "not visible"
occlusion state rather than calling it "unknown", which is technically
more correct.
Bug: chromium:371247941
Change-Id: I4d721dd252d013deac14a12f1f2922830ef2a8a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5950965
Reviewed-by: Xianzhu Wang wangxianzhu@chromium.org
Commit-Queue: Stefan Zager szager@chromium.org
Cr-Commit-Position: refs/heads/main@{#1373093}