Initial implementation of ServiceWorkerGlobalScope.fetch()

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

+self.onmessage = function(e) {
+    var message = e.data;
+    if ('port' in message) {
+        port = message.port;
+        doNextFetchTest(port);
+    }
+};
+
+var testTargets = [
+    'other.html',
+    'http://',
+    'http://www.example.com/foo'
+];
+
+function doNextFetchTest(port) {
+    if (testTargets.length == 0) {
+        port.postMessage('quit');
+        // Destroying the execution context while fetch is happening should not cause a crash.
+        fetch('dummy.html').then(function() {}).catch(function() {});
+        self.close();
+        return;
+    }
+    var target = testTargets.shift();
+    fetch(target)
+    .then(function() {
+        port.postMessage('Resolved: ' + target);
+        doNextFetchTest(port);
+    }).catch(function(e) {
+        port.postMessage('Rejected: ' + target + ' : '+ e.message);
+        doNextFetchTest(port);
+    });
+};