Add example Unity Project

Example Unity Project/Library/PackageCache/com.unity.timeline@1.2.18/Runtime/ILayerable.cs

@@ -0,0 +1,20 @@
+using UnityEngine;
+using UnityEngine.Playables;
+
+namespace UnityEngine.Timeline
+{
+    /// <summary>
+    /// Implement this interface on a TrackAsset derived class to support layers
+    /// </summary>
+    public interface ILayerable
+    {
+        /// <summary>
+        /// Creates a mixer that blends track mixers.
+        /// </summary>
+        /// <param name="graph">The graph where the mixer playable will be added.</param>
+        /// <param name="go">The GameObject that requested the graph.</param>
+        /// <param name="inputCount">The number of inputs on the mixer. There should be an input for each playable from each clip.</param>
+        /// <returns>Returns a playable that is used as a mixer. If this method returns Playable.Null, it indicates that a layer mixer is not needed. In this case, a single track mixer blends all playables generated from all layers.</returns>
+        Playable CreateLayerMixer(PlayableGraph graph, GameObject go, int inputCount);
+    }
+}