Disable system_health.*background:tools:gmail:2019 for android-pixel-2.

Both of these are failing:
system_health.memory_mobile/background:tools:gmail:2019
system_health.common_mobile/background:tools:gmail:2019

NOTRY=true
TBR=crouleau@chromium.org
CC=pasko@chromium.org,crouleau@chromium.org,chrome-android-perf-status@chromium.org,charliea@chromium.org,sullivan@chromium.org,tdresser@chromium.org,chrome-speed-metrics-dev@chromium.org
BUG=1044953

Change-Id: I631729ec70d5a1ebe40c4b31c16b0c71d364ed57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2014911Reviewed-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@{#734435}

tools/perf/expectations.config

@@ -325,6 +325,7 @@ crbug.com/1036141 [ android-webview ] system_health.common_mobile/browse:shoppin
 crbug.com/1036143 [ android-pixel-2 ] system_health.common_mobile/browse:chrome:omnibox:2019 [ Skip ]
 crbug.com/1039801 [ android-webview ] system_health.common_mobile/browse:social:pinterest_infinite_scroll:2019 [ Skip ]
 crbug.com/1044953 [ android-go android-webview ] system_health.common_mobile/load:games:bubbles [ Skip ]
+crbug.com/1044956 [ android-pixel-2 ] system_health.common_mobile/background:tools:gmail:2019 [ Skip ]
 
 # Benchmark: system_health.memory_desktop
 crbug.com/984599 [ linux ] system_health.memory_desktop/long_running:tools:gmail-foreground [ Skip ]
@@ -400,6 +401,7 @@ crbug.com/1036143 [ android-pixel-2 ] system_health.memory_mobile/browse:chrome:
 crbug.com/1036141 [ android-webview ] system_health.memory_mobile/browse:shopping:lazada:2019 [ Skip ]
 crbug.com/1039801 [ android-webview ] system_health.memory_mobile/browse:social:pinterest_infinite_scroll:2019 [ Skip ]
 crbug.com/1044953 [ android-go android-webview ] system_health.memory_mobile/load:games:bubbles [ Skip ]
+crbug.com/1044956 [ android-pixel-2 ] system_health.memory_mobile/background:tools:gmail:2019 [ Skip ]
 
 # Benchmark: tab_switching.typical_25
 crbug.com/747026 [ mac ] tab_switching.typical_25/multitab:misc:typical24 [ Skip ]