Navigation API: ensure that 204/205/downloads never settle

[chromium-wpt-export-bot]

See WICG/navigation-api#137.

This requires distinguishing between "dropped" navigations and other
canceled navigations at the FrameLoader/navigation API interface.

This also makes cross-document ongoing navigations generally abortable,
as can be seen by the revamped navigate-cross-document-double.html test.
Previously, we would clean up the ongoing navigation for any
cross-document nav, but per spec we need to keep it around so that it
can be aborted if someone interrupts it. (This applies both to "normal"
cross-document navigations, and ones to 204s/etc.)

Bug: 1183545
Change-Id: I6f8f1771816ddf454d651f7147d3179fba88979b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3532324
Reviewed-by: Nate Chapin <japhet@chromium.org>
Commit-Queue: Domenic Denicola <domenic@chromium.org>
Auto-Submit: Domenic Denicola <domenic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#984420}

[wpt-pr-bot]

The review process for this patch is being conducted in the Chromium project.

[WeizhongX]

WPT Command: python3 ./wpt run --channel=nightly --verify --verify-no-chaos-mode --verify-repeat-loop=0 --verify-repeat-restart=10 --github-checks-text-file=/home/test/artifacts/checkrun.md --affected base_head --log-mach-level=info --log-mach=- -y --no-pause --no-restart-on-unexpected --install-fonts --no-headless --verify-log-full --binary=/home/test/build/firefox/firefox firefox

Some affected tests had inconsistent (flaky) results:

Unstable results

Test	Subtest	Results	Messages
/navigation-api/ordering-and-transition/navigate-cross-document-double.html		OK: 5/10, TIMEOUT: 5/10
/navigation-api/ordering-and-transition/navigate-cross-document-double.html	event and promise ordering when navigate() is called to a cross-document destination, interrupting another navigate() to a cross-document destination	FAIL: 5/10, TIMEOUT: 5/10	Test timed out;promise_test: Unhandled rejection with value: object "TypeError: can't access property "currentEntry", i.contentWindow.navigation is undefined"

These may be pre-existing or new flakes. Please try to reproduce (see the above WPT command, though some flags may not be needed when running locally) and determine if your change introduced the flake. If you are unable to reproduce the problem, please tag @web-platform-tests/wpt-core-team in a comment for help.

[WeizhongX]

Pinged CL owner at https://chromium-review.googlesource.com/c/chromium/src/+/3532324

@past, can you help admin merge this?

[WeizhongX]

Response from owner: Since Firefox does not implement this API at all, any flakes in Firefox can be disregarded.

[past]

Thanks!