Disabling flaky SystemHealthBenchmarkSmokeTest sheets and maps tests.

Two tests have been flaky:
benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/browse:tools:sheets:2019
benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/browse:tools:maps:2019

Sample run where both failed:
https://ci.chromium.org/p/chromium/builders/ci/Linux%20Tests%20%28dbg%29%281%29/83405

TBR=rmcilroy@chromium.org,perezju@chromium.org

Change-Id: Ifa2362cd6c7553c57dbf34c9dd677c99561c6833
Bug: 1008001
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1825437
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Sebastien Lalancette <seblalancette@chromium.org>
Auto-Submit: Sebastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700205}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -157,6 +157,10 @@ _DISABLED_TESTS = frozenset({
   # crbug.com/978358
   'system_health.memory_desktop/browse:news:flipboard:2018',
 
+  # crbug.com/1008001
+  'system_health.memory_desktop/browse:tools:sheets:2019',
+  'system_health.memory_desktop/browse:tools:maps:2019',
+
   # The following tests are disabled because they are disabled on the perf
   # waterfall (using tools/perf/expectations.config) on one platform or another.
   # They may run fine on the CQ, but it isn't worth the bot time to run them.