private void prepareForBuilding(int chunkIndex) {
      this.chunkIndex = chunkIndex;
      state = ChunkState.Building;
    }
Prepare this chunk for building, that is, for being filled with data from the channel.
@param chunkIndex the position in the overall blob that this chunk is going to  be in.
ambry-router/src/main/java/com/github/ambry/router/PutOperation.java