Moved buffered history system to HDCamera

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Camera/HDAdditionalCameraData.cs

         bool    m_IsDebugRegistered = false;
         string  m_CameraRegisterName;
 
-        BufferedRTHandleSystem m_HistoryRTSystem;
-        public BufferedRTHandleSystem historyRTSystem { get { return m_HistoryRTSystem; } }
-
         // This is the function use outside to access FrameSettings. It return the current state of FrameSettings for the camera
         // taking into account the customization via the debug menu
         public FrameSettings GetFrameSettings()
             }
         }
 
-        void Awake()
-        {
-            m_HistoryRTSystem = new BufferedRTHandleSystem();
-        }
-
         void OnEnable()
         {
             // Be sure legacy HDR option is disable on camera as it cause banding in SceneView. Yes, it is a contradiction, but well, Unity...
         void OnDisable()
         {
             UnRegisterDebug();
-        }
-
-        void OnDestroy()
-        {
-            m_HistoryRTSystem.Dispose();
-            m_HistoryRTSystem = null;
         }
 
         public void OnBeforeSerialize()

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Camera/HDCamera.cs

         HDAdditionalCameraData m_AdditionalCameraData;
 
         // Fallback used when the HDAdditionalCameraData is missing
-        BufferedRTHandleSystem m_HistoryRTSystemFallback = null;
-        public BufferedRTHandleSystem historyRTSystem 
+        BufferedRTHandleSystem m_HistoryRTSystem = null;
+        BufferedRTHandleSystem historyRTSystem 
-                 if (m_AdditionalCameraData == null)
-                 {
-                     if (m_HistoryRTSystemFallback == null)
-                        m_HistoryRTSystemFallback = new BufferedRTHandleSystem();
-                    return m_HistoryRTSystemFallback;
-                 }
-                 return m_AdditionalCameraData.historyRTSystem;
+                if (m_HistoryRTSystem == null)
+                    m_HistoryRTSystem = new BufferedRTHandleSystem();
+                return m_HistoryRTSystem;
              } 
         }
 
             // Unfortunately sometime (like in the HDCameraEditor) HDUtils.hdrpSettings can be null because of scripts that change the current pipeline...
             m_msaaSamples = HDUtils.hdrpSettings != null ? HDUtils.hdrpSettings.msaaSampleCount : MSAASamples.None;
             RTHandles.SetReferenceSize(m_ActualWidth, m_ActualHeight, frameSettings.enableMSAA, m_msaaSamples);
-            historyRTSystem.SetReferenceSize(m_ActualWidth, m_ActualHeight, frameSettings.enableMSAA, m_msaaSamples);
-            historyRTSystem.Swap();
-            
+            if (m_HistoryRTSystem != null)
+            {
+                m_HistoryRTSystem.SetReferenceSize(m_ActualWidth, m_ActualHeight, frameSettings.enableMSAA, m_msaaSamples);
+                m_HistoryRTSystem.Swap();
+            }
 
             int maxWidth = RTHandles.maxWidth;
             int maxHeight = RTHandles.maxHeight;
             foreach (var cam in s_Cleanup)
             {
                 var hdCam = s_Cameras[cam];
-                if (hdCam.m_HistoryRTSystemFallback != null)
+                if (hdCam.m_HistoryRTSystem != null)
-                    hdCam.m_HistoryRTSystemFallback.Dispose();
-                    hdCam.m_HistoryRTSystemFallback = null;
+                    hdCam.m_HistoryRTSystem.Dispose();
+                    hdCam.m_HistoryRTSystem = null;
                 }
                 s_Cameras.Remove(cam);
             }