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Each story in the benchmark does the following:
1. Load the main page.
2. Open and scroll the first news item.
3. Go back to the main page and scroll it.
4. Open and scroll the second news item.
5. Go back to the main page and scroll it.
6. etc.

This workflow is interesting because it is close to real world
and generates a lot of garbage by creating and discarding pages.

A couple of websites crash with OOM on svelte device, so by
tracking and optimizing for this benchmark we can improve
user experience on low-memory devices.

*** NOTE TO SHERRIF ***
Regressions are expected in system_health.memory_mobile and
system_health.memory_desktop for the following stories:
- load:news:cnn
- load:social:facebook
- load:news:qq
- load:news:reddit
- load:social:twitter

If there are failing tests in form of benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.*
please do not revert this CL but instead disabling failing
test by adding them into the _DISABLE_TESTS list in
tools/perf/benchmarks/system_health_smoke_test.py

BUG=589726
CQ_INCLUDE_TRYBOTS=tryserver.chromium.perf:android_s5_perf_cq;tryserver.chromium.perf:mac_retina_perf_cq

Review-Url: https://codereview.chromium.org/2118293002
Cr-Commit-Position: refs/heads/master@{#405212}