Motown: Convert MediaSink to expose MediaTimelineControlSite

mojo/services/media/common/interfaces/timelines.mojom

 // Copyright 2016 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;
 
 // TODO(dalesat): Move out of media to somewhere more generic.
 
 // Used as a placefolder for unspecified time values.
@@ skipping 22 matching lines @@
   // The change in the reference timeline corresponding to subject_delta.
   // Cannnot be zero.
   uint32 reference_delta = 1;
 
   // The change in the subject timeline corresponding to reference_delta.
   uint32 subject_delta = 0;
 };
 
 // A push-mode consumer of timeline updates.
 interface TimelineConsumer {
-  // Sets the timeline transform at the indicated effective time. Exactly one
-  // of the effective_*_time values must be kUnspecifiedTime.
+  // Sets the timeline transform at the indicated effective time. At least one
+  // of the effective_*_time values must be kUnspecifiedTime. If both are
+  // kUnspecifiedTime, the requested change is implemented as soon as possible.
   // effective_subject_time can only be specified if the current subject_delta
   // isn’t zero. reference_delta may not be zero. subject_time may be
   // kUnspecifiedTime to indicate that the new transform subject_time should
-  // be inferred from the effective time. The new transform reference_time is
-  // always inferred from the effective time. The callback is called at the
-  // effective time or when a pending operation is cancelled due to a
-  // subsequent call, in which case the 'completed' value is false.
+  // be inferred from the effective time. The reference time for the new
+  // transform (the reference time that will correspond to the specified or
+  // inferred subject_time) is always inferred from the effective time. The
+  // callback is called at the effective time or when a pending operation is
+  // cancelled due to a subsequent call, in which case the 'completed' value is
+  // false.
   SetTimelineTransform(
       int64 subject_time,
       uint32 reference_delta,
       uint32 subject_delta,
       int64 effective_reference_time,
       int64 effective_subject_time) => (bool completed);
 };