[Telemetry] Make record_wpr more useful.
[Telemetry] Make record_wpr more useful.

1. Record PageSets even if they have no actions.
2. Record PageSets in Measurements and Tests.

BUG=255270,255271
TEST=tools/perf/record_wpr --browser=release pica
NOTRY=True

Review URL: https://chromiumcodereview.appspot.com/18973004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@211305 0039d316-1c4b-4281-b951-d872f2087c98

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