chrome/browser/resources/net_internals/test_view.html

<!-- Connection tests -->
<div id="test-view-tab-content" class="content-box">
  <div style='margin-bottom: 20px'>
    Input a URL which failed to load, and then click the button to run some
    tests for why it failed.
  </div>
  <form id="test-view-connection-tests-form">
    <label>URL: <input id="test-view-url-input" type="text"></label>
    <input id="test-view-connection-tests-submit" type="submit"
        value="Start tests">
  </form>
  <div id="test-view-summary"></div>
</div>