[tools/perf] Disable flaky browse:tech:discourse_infinite_scroll:2018

Same crash in prediction_metrics_handler.cc as other infinite scroll
stories.

NOTRY=true
TBR=crouleau@chromium.org

Bug: 1017661
Change-Id: I902abdf15002e3dcbf93faba0c9c511861724230
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1886852Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710281}

tools/perf/expectations.config

@@ -389,6 +389,7 @@ crbug.com/1002640 [ android-pixel-2 ] system_health.memory_mobile/browse:chrome:
 crbug.com/1002665 [ android-pixel-2 ] system_health.memory_mobile/browse:chrome:omnibox [ Skip ]
 crbug.com/1017661 [ android-nexus-5x ] system_health.memory_mobile/browse:media:flickr_infinite_scroll [ Skip ]
 crbug.com/1017661 [ android-nexus-5x ] system_health.memory_mobile/browse:social:facebook_infinite_scroll:2018 [ Skip ]
+crbug.com/1017661 [ android-nexus-5x ] system_health.memory_mobile/browse:tech:discourse_infinite_scroll:2018 [ Skip ]
 
 # Benchmark: tab_switching.typical_25
 crbug.com/747026 [ mac ] tab_switching.typical_25/multitab:misc:typical24 [ Skip ]