add methods to media source manager

MediaBrowser.Controller/Library/IMediaSourceProvider.cs

@@ -0,0 +1,19 @@
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Model.Dto;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MediaBrowser.Controller.Library
+{
+    public interface IMediaSourceProvider
+    {
+        /// <summary>
+        /// Gets the media sources.
+        /// </summary>
+        /// <param name="item">The item.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        /// <returns>Task&lt;IEnumerable&lt;MediaSourceInfo&gt;&gt;.</returns>
+        Task<IEnumerable<MediaSourceInfo>> GetMediaSources(IHasMediaSources item, CancellationToken cancellationToken);
+    }
+}