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chromium/components/test/data/ads_observer/two_raf_frames.html 

<html>
  <head><title>Iframe with 2 long rAFs</title></head>
  <body>
    <iframe id="test1" src="/ads_observer/expensive_animation_frame.html?delay=200"></iframe>
    <iframe id="test2" src="/ads_observer/expensive_animation_frame.html?delay=200"></iframe>
  </body>
</html>