[mojo-edk] Expose notification source to MojoWatch callbacks

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

 // Copyright 2014 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.
 
 [JavaPackage="org.chromium.mojo.bindings.test.mojom.sample",
  JavaConstantsClassName="InterfaceConstants",
  Foo = "hello world"]
 module sample;
 
 const uint64 kLong = 4405;
@@ skipping 12 matching lines @@
   EchoMessagePipeHandle(handle<message_pipe> a) => (handle<message_pipe> a);
   EchoEnum(Enum a) => (Enum a);
   EchoInt(int32 a) => (int32 a);
 };
 
 interface IntegerAccessor {
   GetInteger() => (int64 data, [MinVersion=2] Enum type);
   [MinVersion=1]
   SetInteger(int64 data, [MinVersion=3] Enum type);
 };
+
+interface SingleMethod {
+  Call();
+};
+
+interface SingleMethodVendor {
+  GetCaller(associated SingleMethod& request);
+};