Add tests for detecting lost associated interfaces.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mojo.test;
 
 import "mojo/public/interfaces/bindings/tests/ping_service.mojom";
 
 interface FooInterface {};
 
@@ skipping 30 matching lines @@
 };
 
 interface IntegerSenderConnection {
   GetSender(associated IntegerSender& sender);
   AsyncGetSender() => (associated IntegerSender sender);
 };
 
 interface AssociatedPingProvider {
   GetPing(associated PingService& request);
 };
+
+interface AssociatedPingProviderProvider {
+  GetPingProvider(associated AssociatedPingProvider& request);
+};