@Override
  public void cacheBlock(BlockCacheKey cacheKey, Cacheable buf) {
    cacheBlock(cacheKey, buf, false);
  }
Cache the block with the specified name and buffer.
<p>
TODO after HBASE-22005, we may cache an block which allocated from off-heap, but our LRU cache
sizing is based on heap size, so we should handle this in HBASE-22127. It will introduce an
switch whether make the LRU on-heap or not, if so we may need copy the memory to on-heap,
otherwise the caching size is based on off-heap.
@param cacheKey block's cache key
@param buf      block buffer
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruBlockCache.java