Add existing to tracked

node_modules/@cesium/engine/Source/Scene/Cesium3DTileContentState.js

@@ -0,0 +1,17 @@
+// @ts-check
+
+/**
+ * @private
+ */
+const Cesium3DTileContentState = {
+  UNLOADED: 0, // Has never been requested
+  LOADING: 1, // Is waiting on a pending request
+  PROCESSING: 2, // Request received.  Contents are being processed for rendering.  Depending on the content, it might make its own requests for external data.
+  READY: 3, // Ready to render.
+  EXPIRED: 4, // Is expired and will be unloaded once new content is loaded.
+  FAILED: 5, // Request failed.
+};
+
+Object.freeze(Cesium3DTileContentState);
+
+export default Cesium3DTileContentState;