code: function ChunkedStreamManager_requestRange(
                        begin, end, callback) {
  
        end = Math.min(end, this.length);
  
        var beginChunk = this.getBeginChunk(begin);
        var endChunk = this.getEndChunk(end);
  
        var chunks = [];
        for (var chunk = beginChunk; chunk < endChunk; ++chunk) {
          chunks.push(chunk);
        }
  
        this.requestChunks(chunks, callback);
      }
docs: Loads any chunks in the requested range that are not yet loaded