code: public ResourcePoolsBuilder offheap(long size, MemoryUnit unit) {
      return with(ResourceType.Core.OFFHEAP, size, unit, false);
    }
docs: Convenience method to add an {@link org.ehcache.config.ResourceType.Core#OFFHEAP offheap} pool.
  
  @param size the pool size
  @param unit the pool size unit
  @return a new builder with the added pool
  
  @throws IllegalArgumentException if the set of resource pools already contains an offheap resource