Disable youtubetv:2020 and twitter:2018 for mac.

each of these are failing 10% of runs for mac-arm_dtk_arm-perf.

Bug: 1163528
Change-Id: I367ced10531dc3cb374170ffcb484dc98567ec35
Cc: mythria@chromium.org,tmrts@chromium.org
No-Try: True
Tbr: johnchen@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2611954Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Commit-Queue: Stephen Nusko <nuskos@chromium.org>
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840608}

tools/perf/expectations.config

@@ -432,6 +432,8 @@ crbug.com/1100138 [ desktop ] v8.browsing_desktop/browse:tools:gmail-search:2020
 crbug.com/1104211 [ win ] v8.browsing_desktop/browse:news:cnn:2020 [ skip ]
 crbug.com/1104211 [ linux ] v8.browsing_desktop/browse:news:cnn:2020 [ skip ]
 crbug.com/1105592 [ desktop ] v8.browsing_desktop/browse:news:nytimes:2020 [ skip ]
+crbug.com/1163528 [ mac ] v8.browsing_desktop/browse:media:youtubetv_watch:2020 [ Skip ]
+crbug.com/1163528 [ mac ] v8.browsing_desktop/browse:social:twitter_infinite_scroll:2018 [ Skip ]
 
 # Benchmark v8.browsing_desktop-future
 crbug.com/788796 [ linux ] v8.browsing_desktop-future/browse:media:imgur [ Skip ]
@@ -451,6 +453,8 @@ crbug.com/1104211 [ win ] v8.browsing_desktop-future/browse:news:cnn:2020 [ skip
 crbug.com/1104211 [ desktop ] v8.browsing_desktop-future/browse:news:cnn:2020 [ skip ]
 crbug.com/1105592 [ desktop ] v8.browsing_desktop-future/browse:news:nytimes:2020 [ skip ]
 crbug.com/1149983 [ win-laptop ] v8.browsing_desktop-future/browse:tools:maps:2019 [ skip ]
+crbug.com/1163528 [ mac ] v8.browsing_desktop-future/browse:media:youtubetv_watch:2020 [ Skip ]
+crbug.com/1163528 [ mac ] v8.browsing_desktop-future/browse:social:twitter_infinite_scroll:2018 [ Skip ]
 
 # Benchmark: v8.browsing_mobile
 crbug.com/958034 [ android-go android-webview ] v8.browsing_mobile/* [ Skip ]