[Benchmarking] Run fewer system health stories on CQ on Android.

This change reduces the number of stories that we run as part of
system_health_smoke_test from 82 to 27. We do this by limiting ourselves
to health_check stories, which are recognized as the most important to
maintain. (Note also that we aren't running all of the 27 since some of
those are currently temporarily disabled.)

Bug: 1019383
Change-Id: I271a0e94288177e9387c9f5551ff44d6e072b9d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888136Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710550}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -309,6 +309,11 @@ def load_tests(loader, standard_tests, pattern):
         story_names=story_names)
 
     for story_to_smoke_test in stories_set.stories:
+      # Per crbug.com/1019383 we don't have many device cycles to work with on
+      # Android, so let's just run the most important stories.
+      if (benchmark_class.Name() == 'system_health.memory_mobile' and
+          'health_check' not in story_to_smoke_test.tags):
+        continue
       suite.addTest(
           _GenerateSmokeTestCase(benchmark_class, story_to_smoke_test))