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chromium/third_party/blink/web_tests/editing/execCommand/change-font.html 

<body contentEditable="true"><font face="Arial">There should only be one font tag.</font></body>
<script src="../editing.js"></script>
<script>
    if (window.testRunner)
        testRunner.dumpAsText();
    var fontNode = document.getElementsByTagName("font")[0];
    setSelectionCommand(fontNode, 0, fontNode, 0);
    execExtendSelectionForwardBySentenceCommand();
    document.execCommand("fontname", false, "Courier");
    var numFontNodes = document.getElementsByTagName("font").length;
    var result = numFontNodes == 1 ? "SUCCESS" : "FAILED";
    document.body.innerHTML += "<p>" + result + "</p>";
</script>