code: public com.google.api.MetricDescriptor.MetricDescriptorMetadata getMetadata() {
      return metadata_ == null ? com.google.api.MetricDescriptor.MetricDescriptorMetadata.getDefaultInstance() : metadata_;
    }
docs: <pre>
  Optional. Metadata which can be used to guide usage of the metric.
  </pre>
  
  <code>.google.api.MetricDescriptor.MetricDescriptorMetadata metadata = 10;</code>