pkg/perf_witness/test/recorder_server_test fails on windows bots

[aam]

https://dart-ci.appspot.com/log/pkg-win-release/unittest-asserts-release-win-x64/35370/pkg/perf_witness/test/recorder_server_test

--- Command "vm" (took 54.000451s):
set DART_CONFIGURATION=ReleaseX64 & set DART_SUPPRESS_WER=1 & set CHROME_PATH=C:\b\s\w\ir\third_party\browsers\chrome\Chrome\Application\chrome.exe & out\ReleaseX64\dart-sdk\bin\dart.exe --enable_asserts -Dtest_runner.configuration=unittest-asserts-release-win-x64 --ignore-unrecognized-flags --packages=C:\b\s\w\ir\.dart_tool\package_config.json C:\b\s\w\ir\pkg\perf_witness\test\recorder_server_test.dart

exit code:
255

stdout:
00:00 [32m+0[0m: Recorder and Server end-to-end test with recorder script[0m

[busy-loop(busy-loop-tag)]stdout> [main] BUSY LOOP READY

[busy-loop(busy-loop-tag)]stdout> [main] AsyncSpan.create is nop: true

[busy-loop(busy-loop-tag)]stdout> [main] AsyncSpan.create is nop: true

[busy-loop(busy-loop-tag)]stdout> [main] AsyncSpan.create is nop: true

[busy-loop(busy-loop-tag)]stdout> [main] AsyncSpan.create is nop: true

[recorder]stdout> Found 0 processes:

[recorder]stdout> ... data will be written to Directory: 'C:\b\s\w\itgp66aeb8\6ec0a65f/output'

00:04 [32m+0[0m[31m -1[0m: Recorder and Server end-to-end test with recorder script [1m[31m[E][0m[0m

  Expected: ['5652.timeline']
    Actual: []
     Which: at location [0] is [] which shorter than expected
  Expected timeline file to be created
  

  package:matcher/src/expect/expect.dart 187:31          fail
  package:matcher/src/expect/expect.dart 182:3           _expect
  package:matcher/src/expect/expect.dart 65:3            expect
  pkg\perf_witness\test\recorder_server_test.dart 177:7  main.<fn>.<fn>
  ===== asynchronous gap ===========================
  package:test_api/src/backend/declarer.dart 253:15      Declarer.test.<fn>.<fn>
  ===== asynchronous gap ===========================
  package:test_api/src/backend/declarer.dart 250:11      Declarer.test.<fn>
  ===== asynchronous gap ===========================
  package:test_api/src/backend/invoker.dart 318:9        Invoker._waitForOutstandingCallbacks.<fn>
  

cc @mraleph