<!DOCTYPE html>
<style>
html {
    scroll-blocks-on: start-touch;
}
iframe {
    position: absolute;
    height: 15px; /* large enough to prevent scrollbars */
    width: 100px;
    border: 0;
}
#f1 {
  top: 20px;
}
#f2 {
  top: 40px;
}
#f3 {
  top: 60px;
}
#f4 {
  top: 80px;
}
</style>
<iframe id=f1 srcdoc="<style>html { scroll-blocks-on: none; }</style>"></iframe>
<iframe id=f2 srcdoc="<style>html { scroll-blocks-on: start-touch; }</style>"></iframe>
<iframe id=f3 srcdoc="<style></style>"></iframe>
<iframe id=f4 srcdoc="<style>html { scroll-blocks-on: start-touch scroll-event; }</style>"></iframe>
<script>
    onload = function() {
        if (window.testRunner) {
            testRunner.dumpAsText();
            var output = "Verify that an iframe will be promoted to a composited layer only when it has additional scroll-blocks-on bits.\n\n";
            output += internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_SCROLL_BLOCKS_ON);
            testRunner.setCustomTextOutput(output);
        }
    };
</script>
