async function buildObjectDetectionModel() {
  const {truncatedBase, fineTuningLayers} = await loadTruncatedBase();

  // Build the new head model.
  const newHead = buildNewHead(truncatedBase.outputs[0].shape.slice(1));
  const newOutput = newHead.apply(truncatedBase.outputs[0]);
  const model = tf.model({inputs: truncatedBase.inputs, outputs: newOutput});

  return {model, fineTuningLayers};
}
Builds object-detection model from MobileNet.

@returns {[tf.Model, tf.layers.Layer[]]}
  1. The newly-built model for simple object detection.
  2. The layers that can be unfrozen during fine-tuning.