moveUpRows_(count) {
    let dst = 0; // Row each row should be moved to.

    // Move existing rows up by <count>.
    for (let i = count; i < shaka.cea.Cea708Window.MAX_ROWS; i++, dst++) {
      this.memory_[dst] = this.memory_[i];
    }

    // Create <count> new rows at the bottom.
    for (let i = 0; i < count; i++, dst++) {
      this.memory_[dst] = this.createNewRow_();
    }
  }
Moves up <count> rows in the buffer.
@param {number} count
@private