third_party/WebKit/LayoutTests/fast/canvas/OffscreenCanvas-multiple-worker-commit.html

<!DOCTYPE>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script id="myWorker" type="text/worker">
self.onmessage = function(e) {
    var offscreenCanvas = e.data;
    var offscreen2d = offscreenCanvas.getContext("2d");
    offscreen2d.commit();
    self.postMessage("worker done");
};
</script>
<script>
function makeWorker() {
   var blob = new Blob([document.getElementById("myWorker").textContent]);
   return new Worker(URL.createObjectURL(blob));
}

// Regression test for crbug.com/663916
async_test(function(t) {
    var canvas1 = document.createElement('canvas');
    canvas1.width = canvas1.height = 10;
    var offscreenCanvas1 = canvas1.transferControlToOffscreen();

    var canvas2 = document.createElement('canvas');
    canvas2.width = canvas2.height = 10;
    var offscreenCanvas2 = canvas2.transferControlToOffscreen();

    var worker1 = makeWorker();
    var worker2 = makeWorker();
    var returnedWorkerCounter = 0;
    worker1.onmessage = worker2.onmessage = function (e) {
        returnedWorkerCounter++;
        if (returnedWorkerCounter == 2)
            t.done();
    };
    worker1.postMessage(offscreenCanvas1, [offscreenCanvas1]);
    worker2.postMessage(offscreenCanvas2, [offscreenCanvas2]);
}, "Calling OffscreenCanvas.commit() from two workers should not crash.");

</script>