[HTMLCanvasElement.toBlob] Default callback version without scheduler

LayoutTests/fast/canvas/canvas-toBlob-case-insensitive-mimetype.html

+<script src = "../../resources/js-test.js"></script>
+<script type = "text/javascript"> 
+if (window.testRunner)
+{
+    testRunner.dumpAsText();
+    testRunner.waitUntilDone();
+}
+
+description("Test that toBlob(mimeType) ignores the case of 'mimeType'.");
+
+canvas = document.createElement('canvas');
+var counter;
+
+function tryMimeType(mimeType, expectedMimeType)
+{
+    canvas.toBlob(function(blob) {
+        if (blob.type === expectedMimeType) {
+            testPassed("");
+        }
+        else {
+            testFailed(blob.type + " does not match " + expectedMimeType);
+        }
+        counter = counter + 1;
+        if (window.testRunner) {
+            if (counter == 8) {

[Justin Novosad, 2015/08/20 20:38:42]

To make the test easier to extend, you should count the number of times
tryMimeType was called, and use that instead of the hard-coded 8.

[xlai (Olivia), 2015/08/20 21:36:28]

Doing that might result in a flaky test. If the blob callback function of the
previous test finishes earlier than the tryMimeType is invoked in the next test,
and I am comparing whether the numbers of calls on both functions "balance" in
order to call notifyDone(), this test set might end up calling notifyDone()
earlier than expected. Right now, although hard-coding is not good looking, the
test can end at exactly the time when it should end.

+                testRunner.notifyDone();
+            }
+        }
+    }, mimeType);
+}
+
+function startTest()

[Justin Novosad, 2015/08/20 20:38:42]

This function does not really serve a purpose. It's code might as well just be
at global scope.

+{
+    counter = 0;

[Justin Novosad, 2015/08/20 20:38:42]

declaration and init can be on same line.

+
+    //Note that due to the async nature of toBlob, these callbacks may complete
+    // at random order but they will all print PASS when they pass.
+    tryMimeType("image/png", "image/png");
+    tryMimeType("iMAge/png", "image/png");
+    tryMimeType("image/PNG", "image/png");

[Justin Novosad, 2015/08/20 20:38:42]

Just one test is enough to verify case insensitivity. You should also add a test
case that verifies that unsupported mime types fall back to png.

[xlai (Olivia), 2015/08/20 21:36:28]

Acknowledged and elsewhere.

+
+    tryMimeType("image/jpeg", "image/jpeg");
+    tryMimeType("imaGE/jpEg", "image/jpeg");
+    tryMimeType("IMAGE/JPEG", "image/jpeg");
+
+    tryMimeType("image/webp", "image/webp");
+    tryMimeType("ImAgE/WeBp", "image/webp");
+}
+
+startTest();
+</Script>