async init(urls) {
    this.urls = urls;
    this.model = await loader.loadHostedPretrainedModel(urls.model);

    // Print model summary right after model is loaded.
    this.model.summary();
    tfVis.show.modelSummary(
        {name: 'Model Summary', tab: 'Model Info'}, this.model);

    this.imageSize = this.model.layers[0].batchInputShape[1];
    this.numClasses = 5;

    await this.loadRetrainData();
    this.prepTestExamples();
    return this;
  }
Initializes the MNIST Transfer CNN demo.