Codebase Browser
chromium
Go to App

chromium/third_party/blink/renderer/core/testing/data/frameserializer/frames/simple_frames_top.html 

<html>
<frameset cols="75%,25%">
    <frame src="simple_frames_1.html">
    <frame src="frame_2.png">
  </frameset>
</frameset>
</html>