Disable very flaky multitab:misc:typical24 on Mac

NOTRY=true

Bug: 828917
Change-Id: I5c36321a1e1ac1c5076e8e3025f9007e47142f73
Reviewed-on: https://chromium-review.googlesource.com/996183
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#548420}

tools/perf/expectations.config

@@ -241,6 +241,7 @@ crbug.com/795060 [ Android_One ] smoothness.tough_texture_upload_cases/extra_lar
 crbug.com/574485 [ Android_Svelte ] smoothness.tough_webgl_ad_cases/* [ Skip ]
 
 # Benchmark: system_health.common_desktop
+crbug.com/828917 [ Mac ] system_health.common_desktop/multitab:misc:typical24 [ Skip ]
 crbug.com/728576 [ Mac ] system_health.common_desktop/browse:news:cnn [ Skip ]
 crbug.com/64939 [ All ] system_health.common_desktop/play:media:pandora [ Skip ]
 crbug.com/809146 [ All ] system_health.common_desktop/browse:media:tumblr [ Skip ]