Disable a flaky perf test

Disable flaky system_health.memory_desktop/browse:news:hackernews:2018
on desktop perf bots.

TBR=crouleau@chromium.org
NOTRY=true

Bug: 1008028
Change-Id: I15b7f313a9c409c1b7a107c4a1f22f5f057d9570
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1826995
Commit-Queue: John Chen <johnchen@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700309}

tools/perf/expectations.config

@@ -353,6 +353,7 @@ crbug.com/942952 [ chromeos ] system_health.memory_desktop/browse:news:hackernew
 crbug.com/959418 [ chromeos ] system_health.memory_desktop/long_running:tools:gmail-background [ Skip ]
 crbug.com/959418 [ chromeos ] system_health.memory_desktop/load:games:spychase:2018 [ Skip ]
 crbug.com/959418 [ chromeos ] system_health.memory_desktop/long_running:tools:gmail-foreground [ Skip ]
+crbug.com/1008028 [ desktop ] system_health.memory_desktop/browse:news:hackernews:2018 [ Skip ]
 
 # Benchmark: system_health.memory_mobile
 crbug.com/1007355 [ android-go android-webview ] system_health.memory_mobile/load:media:imgur:2018 [ Skip ]