- Use unique ptrs for owned objects
- Remove friendship with CpuProfiler and replace with public API
- Remove unused method LogFailure()
- Remove StopProfiler() which was only used by LogFailure() (removed)
  and one test, which can use StopProfilerThread() instead
- Remove 'paused' state which was only used by the above
- Remove 'engage' state. There is no reason we need this as along as
  users keep track of Engage/Disengage calls

Drive-by cleanup:
- Remove import of log.h from profile-generator.h
- Remove unnecessary includes of log.h

Change-Id: Ifc4ca156bef038c40953f8361ffea17788e3a59b
Reviewed-on: https://chromium-review.googlesource.com/c/1424338
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58957}