function LabelVisualizer(entityCluster, entityCollection) {
  //>>includeStart('debug', pragmas.debug);
  if (!defined(entityCluster)) {
    throw new DeveloperError("entityCluster is required.");
  }
  if (!defined(entityCollection)) {
    throw new DeveloperError("entityCollection is required.");
  }
  //>>includeEnd('debug');

  entityCollection.collectionChanged.addEventListener(
    LabelVisualizer.prototype._onCollectionChanged,
    this,
  );

  this._cluster = entityCluster;
  this._entityCollection = entityCollection;
  this._items = new AssociativeArray();

  this._onCollectionChanged(entityCollection, entityCollection.values, [], []);
}
A {@link Visualizer} which maps the {@link LabelGraphics} instance
in {@link Entity#label} to a {@link Label}.
@alias LabelVisualizer
@constructor

@param {EntityCluster} entityCluster The entity cluster to manage the collection of billboards and optionally cluster with other entities.
@param {EntityCollection} entityCollection The entityCollection to visualize.