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chromium/third_party/blink/web_tests/fast/canvas/canvas-fillText-getImageData.html 

<html>
<body>
<canvas id="c" width=50 height=20></canvas>
<script>
var c = document.getElementById('c');
var ctx = c.getContext("2d", {alpha: false});
ctx.fillStyle = "white";
ctx.fillRect(0,0,500,500);
ctx.font = " 20px sans-serif";
ctx.fillStyle = "black";
ctx.fillText("Test", 0, 16);
var imdData = ctx.getImageData(0,0,10,10).data;
</script>
</body>
</html>