Rework beatmap post-processing into HitRenderer.

osu.Game/Beatmaps/IBeatmapProcessor.cs

@@ -0,0 +1,27 @@
+using osu.Game.Modes.Objects;
+
+namespace osu.Game.Beatmaps
+{
+    /// <summary>
+    /// Processes a post-converted Beatmap.
+    /// </summary>
+    /// <typeparam name="T">The type of HitObject contained in the Beatmap.</typeparam>
+    public interface IBeatmapProcessor<T>
+        where T : HitObject
+    {
+        /// <summary>
+        /// Sets default values for a HitObject.
+        /// </summary>
+        /// <param name="hitObject">The HitObject to set default values for.</param>
+        void SetDefaults(T hitObject);
+
+        /// <summary>
+        /// Post-processes a Beatmap to add mode-specific components that aren't added during conversion.
+        /// <para>
+        /// An example of such a usage is for combo colours.
+        /// </para>
+        /// </summary>
+        /// <param name="beatmap">The Beatmap to process.</param>
+        void PostProcess(Beatmap<T> beatmap);
+    }
+}