Add LayoutTests to test Blob URL transfer to {Shared,Service}Workers

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/postmessage-blob-url.js

+self.onmessage = e => {
+  if ('port' in e.data) {
+    let port = e.data.port;
+    port.onmessage = (e) => {
+      fetch(e.data)
+      .then(response => response.text())
+      .then(text => port.postMessage('Worker reply:' + text));
+    };
+    port.postMessage('Connected');
+  }
+};