Codebase Browser
chromium
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chromium/third_party/blink/renderer/core/testing/data/window_dimensions.html 

<!DOCTYPE html>

<meta name="viewport" content="width=1600">
<script>
  var innerWidth = window.innerWidth;
  var innerHeight = window.innerHeight;
  document.write('<div id="output">'+innerWidth+'x'+innerHeight+'</div>');
</script>