@protocol GADRTBAdapter <GADMediationAdapter>
Adapter that provides signals to the Google Mobile Ads SDK to be included in an auction.
Asks the receiver for encrypted signals. Signals are provided to the 3PAS at request time. The receiver must call completionHandler with signals or an error.
This method is called on a non-main thread. The receiver should avoid using the main thread to prevent signal collection timeouts.
func collectSignals(for params: GADRTBRequestParameters, completionHandler: @escaping GADRTBSignalCompletionHandler)