chromium/android_webview/tools/automated_ui_tests/test/data/webview_scroll.html

<!DOCTYPE html>
<html>
  <head>
    <meta name='viewport' content='width=device-width'>
    <title>Scrollable page with select menu in the middle</title>
    <style>
      #select {position:absolute;left:50%;top:50%;}
      #selectbox {position:absolute;width:200%;height:200%;}
    </style>
  </head>
  <body>
    <div id='selectbox'>
      <select id='select'>
        <option value='v1'>Value1</option>
        <option value='v2'>Value2</option>
      </select>
    </div>
  </body>
</html>