Remove stashed request headers for speculative parser tests

[chromium-wpt-export-bot]

The old code would append all of the request headers for the request
to the stashed value. That causes the failure string for all dependent
tests to change when, e.g. the User-Agent string changes due to the
test being run on a different bot.

This CL removes the headers, as those seem only useful for debugging,
and are causing lots of flaky behavior on at least Chromium bots.

Prior failure message:
FAIL Speculative parsing, document.write(): link-rel-stylesheet-disabled Unhandled rejection: assert_equals: speculative case incorrectly fetched expected "" but got "param-encodingcheck: %C4%9E\r\nHost: web-platform.test:8001\nConnection: keep-alive\nUser-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/999.77.34.5 Safari/537.36\nAccept: text/css,/;q=0.1\nReferer: http://web-platform.test:8001/html/syntax/speculative-parsing/generated/document-write/link-rel-stylesheet-disabled.tentative.sub.html\nAccept-Encoding: gzip, deflate\nAccept-Language: en-us,en\n\n"

New failure message:
FAIL Speculative parsing, document.write(): link-rel-stylesheet-disabled Unhandled rejection: assert_equals: speculative case incorrectly fetched expected "" but got "param-encodingcheck: %C4%9E\r\n"

Fixed: 1250457,1249920,1249921,1249954,1250003,1250004
Bug: 1144176
Change-Id: I45dbbb8794c6bf2d5e962cecf531e06a7af09160
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3170927
Commit-Queue: Mason Freed <masonf@chromium.org>
Auto-Submit: Mason Freed <masonf@chromium.org>
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#923491}

[wpt-pr-bot]

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

[mfreed7]

@zcorpan FYI, let me know if you object to this change or want any tweaks. It was causing all kinds of bot grief before this change.

[zcorpan]

@mfreed7 thanks for the ping. The intent is to check that the request headers are equivalent between the speculative fetch and the normal fetch. Is there flake due to the headers being different between speculative fetches and normal fetches? Or flake due to speculative fetches sometimes happening and sometimes not happening?

Maybe we don't need to check all request headers, but a few interesting ones at least (like Origin, Referrer, and other headers that are affected by HTML attributes).

[zcorpan]

If the stashed value is affecting test runs across bots, then that seems like something that shouldn't happen. The UUID is generated for each run of the test (const uuid = token()).

[zcorpan]

Oh wait, I see. Differences in the failure message is interpreted as flake, right?

[mfreed7]

Oh wait, I see. Differences in the failure message is interpreted as flake, right?

Right - when it fails, it (previously) spit out the entire set of request headers, which includes the User-Agent. On Chromium at least, we store away the failure message as an expectation file, and when that same test runs on multiple bots, the error messages will change and cause flakiness. If you want to compare more headers, maybe opt-in the ones you care about?

[zcorpan]

Yes, that makes sense. I can submit a PR in a couple of weeks.