Test non-crashing updating of worker scope event handlers.

LayoutTests/fast/workers/resources/shared-worker-replace-event-handler.js

Index: LayoutTests/fast/workers/resources/shared-worker-replace-event-handler.js
diff --git a/LayoutTests/fast/workers/resources/shared-worker-replace-event-handler.js b/LayoutTests/fast/workers/resources/shared-worker-replace-event-handler.js
new file mode 100644
index 0000000000000000000000000000000000000000..299beb0d24d41933c6423ade7bd4822200250802
--- /dev/null
+++ b/LayoutTests/fast/workers/resources/shared-worker-replace-event-handler.js
@@ -0,0 +1,10 @@
+onconnect = function(event) {
+    function update() {
+        onerror = undefined;
+    }
+    for (var i = 0; i < 8; ++i) {
+        update();
+    }
+    event.ports[0].postMessage("'onerror' repeatedly updated ok.");
+    event.ports[0].postMessage("DONE:");
+};