Example Wordpress Customiser Category Dropdown Control

gistfile1.php

<?php
class WP_Customize_Category_Control extends WP_Customize_Control {
  public $type    = 'dropdown-category';

  public function render_content() {
    $dropdown = wp_dropdown_categories(array(
      "selected"  => $this->value(),
      "name"    => $this->settings["default"]->id,
      "echo"    => 0
    ));

    $dropdown = str_replace( '<select', '<select '.$this->get_link(), $dropdown);

    ?>
     <label>
      <p class="customize-control-title"><?php echo esc_html($this->label);?></p>
      <div><?php echo $dropdown; ?>
      </div>
      </label>
    <?php
  }
}
?>