Add load:search:google:2018 to list of failing system health tests

TBR=perezju@chromium.org

Bug: 964804
Change-Id: Ic9dbdd1cc21982fe99f16c928170456219f37f42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619514Reviewed-by: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#661287}

tools/perf/expectations.config

@@ -322,6 +322,7 @@ crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/load:games:spychase:20
 crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/load:media:flickr:2018 [ Skip ]
 crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/load:news:irctc [ Skip ]
 crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/load:search:baidu:2018 [ Skip ]
+crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/load:search:google:2018 [ Skip ]
 crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/load:tools:stackoverflow:2018 [ Skip ]
 crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/background:search:google [ Skip ]
 crbug.com/964804 [ Nexus_5X ] system_health.memory_mobile/browse:media:googleplaystore:2019 [ Skip ]