Bug 315225 – [Site Isolation] Layout test cross-origin-iframe-request-id-uniqueness.html times out under mac-wk2-stress; skipped pending speedup or harness fix

• Status: NEW
• Component: Web Inspector

[Blaze Burg]

The new layout test
http/tests/site-isolation/inspector/network/cross-origin-iframe-request-id-uniqueness.html,
added by webkit.org/b/310164 to verify deterministic Network IDs across cross-origin iframes
under Site Isolation, is reliably slow and frequently times out under
mac-wk2-stress on EWS.

Cause: the test spawns several processes (one main page + two cross-origin
iframe WebContent processes under Site Isolation, plus an Inspector process)
and waits for inspector-side Frame.ResourceWasAdded events for two separate
fetches. Under stress mode's parallel workers, inter-worker contention on
the shared HTTP server and process launches pushes the test past the
timeout, even with [ Slow ]. Sequential bisect (1 worker) passes 30/30;
the test logic itself is not racy.

Recent EWS run showing the Pass/Timeout pattern:
https://ews-build.webkit.org/#/builders/8/builds/146566

Marking the test as [ Skip ] in platform/mac-wk2/TestExpectations to
unblock the proxy-page-agent stack (PRs #60842, #61172, #61177).
Re-enable when one of:
  - the test is restructured to launch fewer processes, or
  - the test runner / EWS stress configuration handles process-heavy
    Inspector tests without parallel-worker contention.

Observed locally: 29-48% timeout rate with parallel workers; 0% sequential.

[Radar WebKit Bug Importer]

<rdar://problem/177554308>

[Blaze Burg]

Quick archaeology of related-but-not-identical prior art (none addresses process-heavy SI Inspector tests directly):

- webkit.org/b/313791 -- 5 http/tests/inspector constant TIMEOUTs were caused by a build-system symlink issue copying WebInspectorUI resources, not test logic. Different root cause.
- webkit.org/b/313860 -- TestWebKitAPI.WKInspectorExtension flaky timeout fixed by addressing the underlying regression rather than annotating the test. Different surface.
- webkit.org/b/303862 -- Site Isolation mixed-content test failures fixed by replacing determinism-breaking frame load callbacks with setTimeout fallbacks.

The right long-term fix for this test is most likely structural -- consolidate the two iframe scenarios into a single iframe (one cross-origin fetch + one same-origin fetch from the same iframe) so we only spawn one extra WebContent process instead of two, or rewrite the assertion at a layer that does not require launching processes at all (e.g., a unit test of the request-ID assignment logic in the dispatcher).