Add appengine/gcloud/mustache dependencies.

pkg/gcloud/examples/x.dart

+import 'dart:async';
+
+import 'package:googleapis_auth/auth_io.dart' as auth;
+import 'package:gcloud/storage.dart';
+import 'package:gcloud/http.dart';
+import 'package:gcloud/service_scope.dart' as ss;
+
+Future runApp() {
+  // The `runApp` function runs inside a context and can therefore
+  // access any registered values. In this case we use the `storage`
+  // object. But the `authenticatedClient` object is available as well.
+  return storageService.listBucketNames().listen(print).asFuture();
+}
+
+main() {
+  // Assumes we are running on a ComputeEngine VM with the storage scopes
+  // enabled.
+  auth.clientViaMetadataServer().then((httpClient) {
+    // Creates a new context and runs the given closure inside it.
+    ss.fork(() {
+      ss.registerScopeExitCallback(httpClient.close);
+
+      // We register the HTTP client.
+      registerAuthClientService(httpClient);
+
+      // We register the storage object inside the newly created service scope.
+      // This makes it available to all code running inside this context.
+      registerStorageService(new Storage(httpClient, 'my-project-id'));
+      return runApp();
+    });
+  });
+}