[HTMLCanvasElement.toBlob] Default callback version without scheduler

LayoutTests/fast/canvas/canvas-toBlob-defaultpng.html

+<script src = "../../resources/js-test.js"></script>
+<script type = 'text/javascript'>
+description("Test that verifies whether the image data survives the toBlob process");
+
+if (window.testRunner) {
+    testRunner.dumpAsText();
+    testRunner.waitUntilDone();
+}
+
+var canvas = document.createElement("canvas");
+var ctx = canvas.getContext("2d");
+ctx.fillStyle = "#FF0000";
+ctx.fillRect(0, 0, 150, 75);
+var canvas2 = document.createElement("canvas");
+var ctx2 = canvas2.getContext("2d");
+
+var newImg = new Image();
+newImg.onload = function() {
+    ctx2.drawImage(newImg, 0, 0, 150, 75);
+    //Randomly pick a pixel to check whether they match

[Noel Gordon, 2015/08/28 08:53:47]

This doesn't appear to be random pixel pick (it always picks imageData.data[4]).

Since your image is so small (150x75), could you fill the source canvas with
random pixel values, and compare the canvii getImageData.data for all values,
not just .data[4]?

Also is the canvas hardware accelerated (it depends on the canvas size)?  Is
there a toBlob test for the accelerated 2d canvas case?

[xlai (Olivia), 2015/08/28 19:54:19]

Acknowledged for randomized pixel picking. 

+    shouldBe('ctx.getImageData(0, 0, 150, 75).data[4]', 'ctx2.getImageData(0, 0, 150, 75).data[4]');
+    if (window.testRunner)
+        testRunner.notifyDone();
+}
+
+canvas.toBlob(function(blob) {
+    url = URL.createObjectURL(blob);
+    newImg.src = url;
+});
+
+</script>