Motown: Add examples/media_test, a command line media player app.

mojo/services/media/control/interfaces/media_sink.mojom

Index: mojo/services/media/control/interfaces/media_sink.mojom
diff --git a/mojo/services/media/control/interfaces/media_sink.mojom b/mojo/services/media/control/interfaces/media_sink.mojom
index efaa63081b5748e8bc07018b22f990c7c8cc3641..14c2f400ecab89092b45bd1ab11628ae1bf44c18 100644
--- a/mojo/services/media/control/interfaces/media_sink.mojom
+++ b/mojo/services/media/control/interfaces/media_sink.mojom
@@ -18,6 +18,10 @@ import "mojo/services/media/common/interfaces/rate_control.mojom";
 interface MediaSink {
   // TODO(dalesat): Support fanout to many destinations.
 
+  // Special value for GetStatus version_last_seen parameter to get the current
+  // status immediately.
+  const uint64 kInitialStatus = 0;
+
   // Gets the clock disposition from the source.
   GetClockDisposition() => (ClockDisposition clock_disposition);
 
@@ -30,8 +34,9 @@ interface MediaSink {
   // Gets the consumer for the stream to be delivered.
   GetConsumer(MediaConsumer& consumer);
 
-  // Gets the status. To get the status immediately, call GetStatus(0). To
-  // get updates thereafter, pass the version sent in the previous callback.
+  // Gets the status. To get the status immediately, call
+  // GetStatus(kInitialStatus). To get updates thereafter, pass the version
+  // sent in the previous callback.
   GetStatus(uint64 version_last_seen) =>
       (uint64 version, MediaSinkStatus status);