Returns a namespace for JSON serialization of type_obj.

Types can provide custom namespaces with _json_namespace_; otherwise, a Cirq type will not include a namespace in its cirq_type. Non-Cirq types must provide a namespace for serialization in Cirq.

type_obj Type to retrieve the namespace from.

The namespace to prepend type_obj with in its JSON cirq_type.

ValueError if type_obj is not a Cirq type and does not explicitly define its namespace with _jsonnamespace.