Add missing INativeAdLoaderDelegate.

source/Google/MobileAds/ApiDefinition.cs

@@ -1456,6 +1456,23 @@ namespace Google.MobileAds {
 		void DidFinishLoading (AdLoader adLoader);
 	}
 
+	interface INativeAdLoaderDelegate {
+	}
+
+	// @protocol GADNativeAdLoaderDelegate <GADAdLoaderDelegate>
+#if NET
+    [Model]
+#else
+	[Model (AutoGeneratedName = true)]
+#endif
+	[Protocol]
+	[BaseType (typeof (NSObject), Name = "GADNativeAdLoaderDelegate")]
+	interface NativeAdLoaderDelegate : AdLoaderDelegate {
+		// @optional - (void)adLoader:(nonnull GADAdLoader *)adLoader didReceiveNativeAd:(nonnull GADNativeAd *)nativeAd;
+		[Export("adLoader:didReceiveNativeAd:")]
+		void DidReceiveNativeAd (AdLoader adLoader, NativeAd nativeAd);
+	}
+
 	#region Loading.Formats
 
 	interface INativeAdDelegate {