Currently the InitialMetricsLog is a bit complicated to reason about.

* When metrics is first enabled, the first ONGOING metrics log is created, and made current.
* After the init task is finished, the InitialMetricsLog is created, but NOT made current.
* When the first log rotation occurs shortly after this, the ongoing log is paused, and some data is written to the InitialMetricsLog.

This all means that the period of time the first logs cover is somewhat ambiguous.  InitialMetricsLog will contain histograms and callstacks and profiler data from before it was created, but contains no user actions.

This could probably all be simplified to just make InitialMetricsLog cover everything from startup, and the first ONGOING log to cover everything after that.