chromium/chrome/renderer/resources/plugins/pdf_plugin.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport"
      content="initial-scale=1, minimum-scale=1, width=device-width">
    <script>
      // If this page is embedded in a WebViewPlugin, the 'window.plugin'
      // object is externally defined, and we trigger the download that way.
      if (window.plugin !== undefined) {
        window.addEventListener('DOMContentLoaded', function () {
          let button = document.getElementById('open-button');
          button.addEventListener('click', function(e) {
            window.plugin.openPDF();
            e.preventDefault();
          });

          if (plugin.notifyPlaceholderReadyForTesting)
            plugin.notifyPlaceholderReadyForTesting();
        });
      }

      window.onkeydown = function(e) {
        if (e.key == 'Enter' || e.key == ' ') {
          document.getElementById('open-button').click();
          e.preventDefault();
        }
      };
    </script>
    <link rel="stylesheet" href="../../../../components/security_interstitials/core/common/resources/interstitial_core.css">
    <link rel="stylesheet" href="../../../../components/security_interstitials/core/common/resources/interstitial_common.css">
    <link rel="stylesheet" href="../../../../components/security_interstitials/core/browser/resources/interstitial_webview_quiet.css">
    <style>
      path {
        fill-opacity: 0.2;
      }

      .icon {
        background-image: none;
      }

      button,
      [dir='rtl'] button {
        float: none;
      }
    </style>
  </head>
  <body class="pdf">
    <div class="interstitial-wrapper">
      <div id="main-content">
        <div class="icon">
          <!-- Material Design PDF icon -->
          <svg viewBox="0 0 24 24">
            <path d="M7 11.5h1v-1H7v1zM19 3H5c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h14c1.1 0 2-.9 2-2V5c0-1.1-.9-2-2-2zm-9.5 8.5c0 .83-.67 1.5-1.5 1.5H7v2H5.5V9H8c.83 0 1.5.67 1.5 1.5v1zm10-1H17v1h1.5V13H17v2h-1.5V9h4v1.5zm-5 3c0 .83-.67 1.5-1.5 1.5h-2.5V9H13c.83 0 1.5.67 1.5 1.5v3zm-2.5 0h1v-3h-1v3z"></path>
          </svg>
        </div>
        <div id="main-message">
          <h1>$i18n{fileName}</h1>
        </div>
        <a href="$i18n{pdfUrl}" target="_blank">
          <button id="open-button" tabindex="1">$i18n{open}</button>
        </a>
      </div>
    </div>
  </body>
</html>