It makes a lot of test to pass by ensuring the isolated tree is updated before being queried in the a11y thread
Created attachment 448575 [details] Patch
Comment on attachment 448575 [details] Patch Clearing flags, this has other side effect, I'll continue investigating the issue.
Created attachment 448741 [details] Patch
Committed r287872 (?): <https://commits.webkit.org/r287872>