Reland "navigate-iframe-out2in.js test: use map to handle duplicate events"

This is a reland of commit 1ee52f5e90d486fe43d9e04abcf09d6c987c0510

Original change's description:
> navigate-iframe-out2in.js test: use map to handle duplicate events
>
> This test has been flaky on Mac bots, because sometimes there would be
> multiple duplicate events polluting the test output. Using a map
> allows us to deduplicate these events.
>
> Bug: 40255790
> Change-Id: Ia950630e9a2c8c5f8695c184d72a3d022a181b81
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6218792
> Commit-Queue: Wolfgang Beyer <wolfi@chromium.org>
> Reviewed-by: Danil Somsikov <dsv@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1415592}

Bug: 40255790
Change-Id: Ie9829b1921895a941b9c890734fb8769fa9ea705
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6275134
Reviewed-by: Danil Somsikov <dsv@chromium.org>
Commit-Queue: Wolfgang Beyer <wolfi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1421261}