Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/shelf/example/example_server.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:shelf/shelf.dart' as shelf;
+import 'package:shelf/shelf_io.dart' as io;
+
+void main() {
+  var handler = const shelf.Pipeline()
+      .addMiddleware(shelf.logRequests())
+      .addHandler(_echoRequest);
+
+  io.serve(handler, 'localhost', 8080).then((server) {
+    print('Serving at http://${server.address.host}:${server.port}');
+  });
+}
+
+shelf.Response _echoRequest(shelf.Request request) {
+  return new shelf.Response.ok('Request for "${request.url}"');
+}