private void StartVisualTreeAssetTracking(ILiveReloadAssetTracker <VisualTreeAsset> tracker, VisualTreeAsset asset)
        {
            int dirtyCount = tracker.StartTrackingAsset(asset);

            if (!m_AssetToTrackerMap.TryGetValue(asset, out var trackers))
            {
                trackers = new VisualTreeAssetToTrackMappingEntry()
                {
                    m_LastDirtyCount                    = dirtyCount,
                    m_LastElementCount                  = asset.visualElementAssets.Count,
                    m_LastInlinePropertiesCount         = asset.inlineSheet.rules.Sum(r => r.properties.Length),
                    m_LastAttributePropertiesDirtyCount = asset.GetAttributePropertiesDirtyCount(),
                    m_Trackers = new HashSet <ILiveReloadAssetTracker <VisualTreeAsset> >()
                };
                m_AssetToTrackerMap[asset] = trackers;
            }
            trackers.m_Trackers.Add(tracker);
        }