Repro steps:

third_party/WebKit/Tools/Scripts/run-webkit-tests -t gn-debug --additional-driver-flag=--site-per-process http/tests/serviceworker/http-to-https-redirect-and-register.html --driver-logging --full-results-html

After digging into the test, it appears that it's failing because the test incorrectly relies on a couple of events arriving in a certain order, which isn't holding with OOPIFs.  Specifically, the second promise_test adds a cross-origin iframe, which registers a ServiceWorker.  When that registration finishes, a postMessage is sent to the parent frame.  Meanwhile, the parent frame waits for the frame's onload to fire, then installs an onmessage handler which will finish the test upon receiving a message.  With --site-per-process, the ServiceWorker registration postMessage arrives before the onload fires, and since there's no onmessage handler registered yet, we lose that message.

To sum up, this seems to be a test issue that can be fixed with some reordering in the test logic.