createHeader_(parentDiv, headerText) {
    if (this.style_ == shakaDemo.InputContainer.Style.ACCORDION) {
      this.header_ = document.createElement('button');
      this.header_.classList.add('mdl-button--raised');
      this.header_.classList.add('mdl-button');
      this.header_.classList.add('mdl-js-button');
      this.header_.classList.add('mdl-js-ripple-effect');
      this.header_.addEventListener('click', () => {
        // Show/hide the table.
        if (this.getIsOpen()) {
          this.close();
        } else {
          this.open();
        }
      });
    } else {
      this.header_ = document.createElement('div');
      this.header_.classList.add('input-header');
    }
    this.header_.textContent = headerText;
    parentDiv.appendChild(this.header_);
  }
@param {!Element} parentDiv
@param {string} headerText
@private