CSP3: Implement 'worker-src'.

third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/ping.js

+if (typeof ServiceWorkerGlobalScope === "function") {
+  self.onmessage = function (e) { e.source.postMessage("ping"); };
+} else if (typeof SharedWorkerGlobalScope === "function") {
+  onconnect = function (e) {
+    var port = e.ports[0];
+
+    port.onmessage = function () { port.postMessage("ping"); }
+    port.postMessage("ping");
+  };
+} else if (typeof DedicatedWorkerGlobalScope === "function") {
+  self.postMessage("ping");
+}