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

mojo/services/media/control/interfaces/media_player.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.
 
 [DartPackage="mojo_services"]
 module mojo.media;
 
 import "mojo/services/media/common/interfaces/media_metadata.mojom";
 import "mojo/services/media/common/interfaces/media_state.mojom";
 import "mojo/services/media/common/interfaces/rate_control.mojom";
 
 // Plays media.
 interface MediaPlayer {
+  // Special value for GetStatus version_last_seen parameter to get the current
+  // status immediately.
+  const uint64 kInitialStatus = 0;
+
   // Starts playback.
   Play();
 
   // Pauses playback.
   Pause();
 
   // Seeks to the specified position, specified in nanoseconds.
   // TODO(dalesat): Consider adding relative vs remote flag.
   // TODO(dalesat): Consider adding parameters regarding desired precision.
   Seek(int64 position);
 
-  // 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, MediaPlayerStatus status);
 };
 
 // MediaPlayer status information.
 struct MediaPlayerStatus {
   // Current state of the player.
   MediaState state;
 
   // Transform translating local time to presentation time. Reverse translation
   // (presentation time to local time) is only valid when media is playing.
   TimelineTransform? timeline_transform;
 
   // Describes the media.
   MediaMetadata? metadata;
 };