title: How to pass extension function as argument?
body: <p>There is an extension functions</p>
  <pre class="lang-kotlin prettyprint-override"><code>fun List&lt;Track&gt;.sortByTitle(): List&lt;Track&gt; {
      return this.sortedBy { it.title }
  }
  
  fun List&lt;Track&gt;.sortByArtist(): List&lt;Track&gt; {
      return this.sortedBy { it.artists[0].name }
  }
  </code></pre>
  <p>What need to write in arguments of <code>sort</code> function in order to pass an extension function?</p>
  <pre><code>fun sortByTitle(owner: String, kind: String) {
      sort(owner, kind) // pass List&lt;Track&gt;.sortByTitle
  }
  
  fun sortByArtist(owner: String, kind: String) {
      sort(owner, kind) // pass List&lt;Track&gt;.sortByArtist
  }
  
  private fun sort(owner: String, kind: String) {
      val remote = playlist.get(owner, kind)
      val tracks = // call extension function: remote.tracks.sortByTitle()
      // ...
  }
  </code></pre>