[HDRenderPipelineEditor] Use serialization callback instead of OnValidate to copy runtime data

ScriptableRenderPipeline/HDRenderPipeline/HDRP/HDRenderPipelineAsset.cs

-namespace UnityEngine.Experimental.Rendering.HDPipeline
+namespace UnityEngine.Experimental.Rendering.HDPipeline
-    public class HDRenderPipelineAsset : RenderPipelineAsset
+    public class HDRenderPipelineAsset : RenderPipelineAsset, ISerializationCallbackReceiver
     {
         HDRenderPipelineAsset()
         {
             return m_FrameSettings;
         }
 
-        public void OnEnable()
-        {
-            // At creation we need to copy serializedFrameSettings to m_FrameSettings
-            OnValidate();
-        }
-
-        public void OnValidate()
-        {
-            // Modification of defaultFrameSettings in the inspector will call OnValidate().
-            // We do a copy of the settings to those effectively used
-            serializedFrameSettings.CopyTo(m_FrameSettings);
-
-            // All instance created in the editor have obsolete settings
-            // So we must dispose them
-            DestroyCreatedInstances();
-        }
-
         // Store the various RenderPipelineSettings for each platform (for now only one)
         public RenderPipelineSettings renderPipelineSettings = new RenderPipelineSettings();
 
 
         [SerializeField]
         public SubsurfaceScatteringSettings sssSettings;
+        ISerializationCallbackReceiver m_SerializationCallbackReceiverImplementation;
 
         public override Shader GetDefaultShader()
         {
         public override Material GetDefault2DMaterial()
         {
             return null;
+        }
+
+        void ISerializationCallbackReceiver.OnBeforeSerialize()
+        {
+        }
+
+        void ISerializationCallbackReceiver.OnAfterDeserialize()
+        {
+            // Modification of defaultFrameSettings in the inspector will call OnValidate().
+            // We do a copy of the settings to those effectively used
+            serializedFrameSettings.CopyTo(m_FrameSettings);
         }
     }
 }