“An origin trial can enable the RuntimeFeature, which will allow full access to the API, provided the base::Feature is also enabled (see change to origin_trial_context.cc).”
Web Environment Integrity is supposedly a proposal up for debate. This commit landed in Chromium on July 21 with five reviewers signed off, wiring the API so an origin trial switches it on in full. Google keeps a Finch kill-switch for itself. Users get no switch at all.