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Some sites, notably techcrunch, in top25 were failing to reach readyState
complete or quiesence due to continual requests (possibly an artifact of
the wpr). As this benchmark normalizes/categories results, it shouldn't
be necessary to reach the same state on every run.

Also switches to a tighter tracing category which allows the reference build
to be re-enabled, since the metrics will not appear there until they are
valid to be consumed by the blink_style measurement.

BUG=479048

Review URL: https://codereview.chromium.org/1100853003

Cr-Commit-Position: refs/heads/master@{#327235}