The human-readable output of sam_metadata_dumper uses the old-style metadata keys, fileType, dataTier and streamName; the JSON output features file_type, data_tier and data_stream, per their SAM equivalents. applicationFamily and applicationVersion remain camel-case because they have no direct SAM equivalents: they must be combined with the application name as part of a tuple. See the sam-web wiki metadata article for more details.
file_type (or fileType) is correctly output as, "unknown" if not specified by command-line or FHiCL. If file_type is added by user code, then the duplicate key will appear later in the output list and therefore, by convention, be considered to override.
art::SourceHelper::make_ptr -> art::SourceHelper::makePtr for consistency of interface.