As part of the investigation for bug 1523307 and bug 1505395, it was discovered that all specific metrics that Glean generates are put in a single namespace (mozilla.components.service.glean.metrics.) and everything in there is public. This means that in our multi-libraries-using-Glean future, any library can modify or report to any metric defined by any other library or application, including Glean itself.

So support good code encapsulation, we should generate the metrics to reside in the namespace of the library or application in which the metrics are defined, and make everything in there internal.