[tools/perf] Disable flaky background:news:nytimes

Story has been flaky in system_health.memory_mobile when running as
smoke test on N5X.

NOTRY=true
TBR=nednguyen@google.com

Bug: 852888
Change-Id: I8f82f42d50c6bf5f34bfda1cc42d147444921c05
Reviewed-on: https://chromium-review.googlesource.com/1109512Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569191}

tools/perf/expectations.config

@@ -389,6 +389,7 @@ crbug.com/834905 [ Nexus_5 ] system_health.memory_mobile/browse:social:pinterest
 crbug.com/842731 [ Android_One ] system_health.memory_mobile/background:news:nytimes [ Skip ]
 crbug.com/843547 [ Android_Go ] system_health.memory_mobile/background:news:nytimes [ Skip ]
 crbug.com/852840 [ Android_Webview ] system_health.memory_mobile/browse:media:youtube [ Skip ]
+crbug.com/852888 [ Nexus_5X ] system_health.memory_mobile/background:news:nytimes [ Skip ]
 
 # Benchmark: tab_switching.typical_25
 crbug.com/747026 [ Mac ] tab_switching.typical_25/multitab:misc:typical24 [ Skip ]