Skeleton for BackgroundTracingManager.
This version mostly just directs the TracingController using the specified BackgroundTracingConfig and pushes the compressed trace out to the BackgroundTracingUploadSink.
Specifically, we implement the PREEMPTIVE_TRACING_MODE for the rule MONITOR_AND_DUMP_WHEN_TRIGGER_NAMED, which should allow us to get an experiment going on desktop with a simple trigger and upload.
We can then follow up with additional CL's implementing the rest of the functionality from the clientside doc below.
Needs to land first: https://codereview.chromium.org/
1088673003/
Slow Reports Clientside: https://docs.google.com/document/d/1qZmXmodxOKmsTRO27z2WlH2h9Kpf-kjV-k-1pJIogIE/edit?pli=1
go/slow-reports
Review URL: https://codereview.chromium.org/
1089253003
Cr-Commit-Position: refs/heads/master@{#330942}