Implement Asynchronous image encoding for Canvas.toBlob

third_party/WebKit/LayoutTests/fast/canvas/script-tests/canvas-toBlob-toDataURL-race.js

+if (window.testRunner) {
+    testRunner.dumpAsText();
+    testRunner.waitUntilDone();
+}
+
+var numToBlobCalls = 9;
+var numToDataURLCalls = 3;
+var testImages = [];
+var canvasCtxs = [];
+
+// Create an original canvas with content
+var canvas = document.createElement("canvas");
+var ctx = canvas.getContext("2d");
+ctx.fillStyle = "#EE21AF";
+ctx.fillRect(0, 0, 2500, 1750);
+
+function testIfAllImagesAreCorrect()
+{
+    // All resultant images should be the same as both async and main threads use the same image encoder
+    var imageMatched = true;
+    var firstImageData = canvasCtxs[0].getImageData(0, 0, 2500, 1750).data;
+    for (var i = 1; i < (numToBlobCalls + numToDataURLCalls); i++) 
+    {
+        var nextImageData = canvasCtxs[i].getImageData(0, 0, 2500, 1750).data;
+        for (var k = 0; k < firstImageData.length; k++) 
+        {
+            if (firstImageData[k]!=nextImageData[k]) 
+            {
+                imageMatched = false;
+                break;
+            }
+        } 
+        if (!imageMatched) 
+            break;
+    }
+    if (imageMatched)
+        testPassed("All images encoded by both async and main threads match one another");
+    else 
+        testFailed("Not all images encoded by async and main threads match one another");
+}
+
+var counter = numToBlobCalls + numToDataURLCalls;
+function onCanvasDrawCompleted(ctx_test) 
+{
+    counter = counter - 1;
+    if (counter == 0) {
+        testIfAllImagesAreCorrect();
+        if (window.testRunner)
+            testRunner.notifyDone();
+    } 
+}
+
+function createTestCase(i)
+{
+    var canvas_test = document.createElement("canvas");
+    var ctx_test = canvas_test.getContext("2d");
+    canvasCtxs[i] = ctx_test;
+
+    var newImg = new Image();
+    newImg.onload = function() {
+        ctx_test.drawImage(newImg, 0, 0, 2500, 1750);
+        onCanvasDrawCompleted(ctx_test);
+    }    
+    testImages[i] = newImg;
+}
+
+for (var i = 0; i < (numToBlobCalls + numToDataURLCalls); i++) 
+{
+    createTestCase(i);
+}