[FedCM] Ignore unexpected messages
Webdriver internally uses testdriver-complete messages.
We should ignore them when waiting for messages from our
iframe.
This fixes the three changed tests on wpt.fyi.
Bug: 331237776
Change-Id: Id274b724d5974b646f1ca4c389820befc9072109
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5721452
Reviewed-by: Nicolás Peña npm@chromium.org
Commit-Queue: Christian Biesinger cbiesinger@chromium.org
Auto-Submit: Christian Biesinger cbiesinger@chromium.org
Cr-Commit-Position: refs/heads/main@{#1330510}