Freeze global prototype chain per WebIDL

third_party/WebKit/LayoutTests/security/immutable-prototype-worker.js

+importScripts('immutable-prototype.js');
+
+if (!self.postMessage) {
+  // This is a shared worker - mimic dedicated worker APIs
+  onconnect = function(event) {
+    event.ports[0].onmessage = function(e) {
+      self.postMessage = function (msg) {
+        event.ports[0].postMessage(msg);
+      };
+      run();
+    };
+  };
+} else {
+  run();
+}
+
+function run() {
+  self.postMessage(prototypeChain(self));
+}