Fetcher: Disable memory caching when Service Worker handles a request

LayoutTests/http/tests/serviceworker/chromium/resources/memory-cache-worker.js

+var port;
+
+var promise = new Promise(function(resolve, reject) {
+    self.onmessage = function(e) {
+      var message = e.data;
+      if ('port' in message) {
+        port = message.port;
+      } else if ('ping' in message) {
+        resolve();
+      } else {
+        reject();
+      }
+    }
+  });
+
+onfetch = function(event) {
+  if (event.request.url.indexOf('memory-cache.json') != -1) {
+    event.respondWith(promise.then(function() {
+        return new Response("callback({ src : 'service worker' })");
+      }));
+    port.postMessage('ack');
+  }
+}