title: Hook to change page title
body: <p>I want to programmatically alter a page title in Drupal 8 so that it will be hard-coded in the theme file.</p>
  
  <p>I'm attempting to use a hook function to preprocess_page_title, but it seems to not understand what page to change the title on.</p>
  
  <p>Here's what I have so far:</p>
  
  <pre><code>function test_preprocess_page_title(&amp;$variables) {
    if (arg(0) == 'node/12') {
      $variables['title'] = 'New Title';
    }
  }
  </code></pre>
  
  <p>I figured the only way to make this change on one specific page is to set the node argument. Has any one figured out a way to override page title on Drupal?</p>