Add tests for detecting lost associated interfaces.

mojo/public/interfaces/bindings/tests/test_associated_interfaces.mojom

Index: mojo/public/interfaces/bindings/tests/test_associated_interfaces.mojom
diff --git a/mojo/public/interfaces/bindings/tests/test_associated_interfaces.mojom b/mojo/public/interfaces/bindings/tests/test_associated_interfaces.mojom
index a5ae0dcf9747733fa4bffe821e3e2d3d3ab8ed3f..adc4e7e809e91d79e9bfdc4d95acdbe0edb95c93 100644
--- a/mojo/public/interfaces/bindings/tests/test_associated_interfaces.mojom
+++ b/mojo/public/interfaces/bindings/tests/test_associated_interfaces.mojom
@@ -48,3 +48,7 @@ interface IntegerSenderConnection {
 interface AssociatedPingProvider {
   GetPing(associated PingService& request);
 };
+
+interface AssociatedPingProviderProvider {
+  GetPingProvider(associated AssociatedPingProvider& request);
+};