Track feature flag name

[reillyeon]

Related to #1209 but also generally useful for other kind of tracking, the ChomeStatus tool should have a field for the Blink flag (from runtime_enabled_features.json5) and/or base::Feature flag for the feature and whether this flag is exposed through about:flags.

This could be used to build a pipeline to understand based on release branches whether a feature is launching in a particular release and to flag instances where a feature is pulled back at the last minute.

[jrobbins]

We currently have a flag_name field, but that is it.