Add existing to tracked

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

@@ -0,0 +1,28 @@
+/**
+ * A {@link TileDiscardPolicy} specifying that tile images should never be discard.
+ *
+ * @alias NeverTileDiscardPolicy
+ * @constructor
+ *
+ * @see DiscardMissingTileImagePolicy
+ */
+function NeverTileDiscardPolicy(options) {}
+
+/**
+ * Determines if the discard policy is ready to process images.
+ * @returns {boolean} True if the discard policy is ready to process images; otherwise, false.
+ */
+NeverTileDiscardPolicy.prototype.isReady = function () {
+  return true;
+};
+
+/**
+ * Given a tile image, decide whether to discard that image.
+ *
+ * @param {HTMLImageElement} image An image to test.
+ * @returns {boolean} True if the image should be discarded; otherwise, false.
+ */
+NeverTileDiscardPolicy.prototype.shouldDiscardImage = function (image) {
+  return false;
+};
+export default NeverTileDiscardPolicy;