chromium/src/third_party/blink/web_tests/fast/canvas/canvas-filter-width-height-hidpi-scale-expected.html

<canvas id="canvas" width="100" height="100"></canvas>
<script>
function runTest() {
    if (window.testRunner) {
        testRunner.waitUntilDone();
        testRunner.setBackingScaleFactor(2, function() {
            var canvas = document.getElementById('canvas');
            canvas.style.width = '50px';
            canvas.style.height = '50px';
            var ctx = canvas.getContext('2d');
            ctx.fillStyle = '#0f0';
            ctx.fillRect(0, 0, 50, 40);
            testRunner.notifyDone();
        });
    }
}

window.onload = runTest;
</script>