[Blink-WebWorkers] WorkerSharedTimer cancels extra delayed tasks.

LayoutTests/fast/workers/resources/worker-timeout-decreasing-order.js

+self.postMessage("Test started.");
+// The test will create 3 timeouts with their intervals decreasing.
+// If the timeouts execute in order then the test is PASS.
+self.addEventListener('message', function(e) {
+    setTimeout(function () { postMessage(3); postMessage("DONE"); }, 15);
+    setTimeout(function () { postMessage(2); }, 10);
+    setTimeout(function () { postMessage(1); }, 5);
+}, false);