The party that generated this notification, which can take the
following value: - GOOGLE: this notification as generated by Google.
Note that the value of NSRC_GOOGLE has been deprecated in favor of
GOOGLE.
Values:
UNDEFINED_SOURCE (0):
A value indicating that the enum field is not
set.
GOOGLE (497439289):
This notification was generated by Google.
NSRC_GOOGLE (510574562):
[Deprecated] This notification was generated by Google.