getFeatures() {
    let features;
    if (this.featuresCollection_) {
      features = this.featuresCollection_.getArray().slice(0);
    } else if (this.featuresRtree_) {
      features = this.featuresRtree_.getAll();
      if (!isEmpty(this.nullGeometryFeatures_)) {
        extend(features, Object.values(this.nullGeometryFeatures_));
      }
    }
    return features;
  }
Get a snapshot of the features currently on the source in random order. The returned array
is a copy, the features are references to the features in the source.
@return {Array<FeatureType>} Features.
@api