Wait on the chevron transition in the drawer test
The browser lane of the run on main (2e4d106c) failed in tests/browser/test-drawer-headers.test.js with "Chevron transform did not settle". The test counted animation frames under a 1500 ms wall-clock deadline. On a loaded runner frames arrive seconds apart: in a local repro, three frames took about 6.5 s, so the deadline expired although the 140 ms CSS transition had finished.
The helper now reads the computed style to start the transition, then waits for the element's own animations to finish, bounded by a 5 s timeout that names the failure. It no longer depends on frame cadence. No product code changes.
Validation: before the change the test failed in 3 of about 20 local runs; after it, 18 runs passed with 0 failures. I did not run the full scripts/test.sh, so the CI result is still to come.
Summary by cubic
Fixes the flaky drawer header test on main that failed with "Chevron transform did not settle" on loaded runners. The old helper counted animation frames under a 1500 ms deadline; on a loaded runner frames arrive seconds apart, so the deadline expired even though the 140 ms CSS transition had finished. The helper now reads the computed style to start the transition, then waits for the element's animations with a 5 s timeout that names the failure. No product code changes.
Validation
- Failed in 3 of ~20 local runs before; passed 18 runs after.