Enum describing available third party integration partners for YouTube viewability verification.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v24/enums/third_party_viewability_integration_partner.proto)

| Enums ||
|---|---|
| ## `DOUBLE_VERIFY` | DoubleVerify. |
| ## `INTEGRAL_AD_SCIENCE` | Integral Ad Science. |
| ## `UNKNOWN` | Used for return value only. Represents value unknown in this version. |
| ## `UNSPECIFIED` | Not specified. |
| ## `ZEFR` | Zefr. |