code: private static void addDescriptor(List<String> descriptors, ServiceDescriptor serviceDescriptor) {
      for (MethodDescriptor<?, ?> method : serviceDescriptor.getMethods()) {
        // This is added by Cloud Bigtable's AbstractRetryingOperation
        descriptors.add("Operation." + method.getFullMethodName().replace('/', '.'));
      }
    }
docs: Reads a list of {@link MethodDescriptor}s from a {@link ServiceDescriptor} and creates a list
  of Open Census tags.
  
  @param descriptors a {@link} of Strings to add Open Census tags to
  @param serviceDescriptor A {@link ServiceDescriptor} that contains a list of RPCs that are
  provided by that service