Initial implementation of ServiceWorkerGlobalScope.fetch()

LayoutTests/http/tests/serviceworker/resources/fetch-event-test-worker.js

 function handleHelloWorld(event) {
     event.respondWith(new Response(new Blob(["hello, world"])));
 }
 
 function handleNullBody(event) {
     event.respondWith(new Response(null));
 }
 
 function handleReject(event) {
     event.respondWith(new Promise(function(resolve, reject) {
         reject('rejected!');
     }));
 }
 
+function handleFetch(event) {
+    event.respondWith(fetch('other.html'));
+}
+
 self.addEventListener('fetch', function(event) {
     var url = event.request.url;
     var handlers = [
         { pattern: 'helloworld', fn: handleHelloWorld },
         { pattern: '?ignore', fn: function() {} },
         { pattern: '?null', fn: handleNullBody },
-        { pattern: '?reject', fn: handleReject }
+        { pattern: '?reject', fn: handleReject },
+        { pattern: '?fetch', fn: handleFetch }
     ];
 
     var handler = null;
     for (var i = 0; i < handlers.length; ++i) {
        if (url.indexOf(handlers[i].pattern) != -1) {
            handler = handlers[i];
            break;
        }
     }
 
     if (handler)
         handler.fn(event);
     else
         event.respondWith(new Response(new Blob(['Service Worker got an unexpected request: ' + url])));
 });