Javascript setTimeout can be used for high resolution clock
Using Javascript setTimeout, around 20ms timer resolution can be achieved. This is likely sufficient for input fingerprinting.
Simple demo that logs a counter to the console.
<html>
<body onload="logTime()">
<p>Test</p>
<script>
var counter = 0;
function logTime() {
counter += 1;
var today = new Date();
console.log(today.getSeconds() + "." + today.getMilliseconds() + " " + counter);
var t = setTimeout(logTime, 1);
}
</script>
</body>
</html>