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

mojo/public/dart/third_party/csslib/bin/css.dart

Index: mojo/public/dart/third_party/csslib/bin/css.dart
diff --git a/mojo/public/dart/third_party/csslib/bin/css.dart b/mojo/public/dart/third_party/csslib/bin/css.dart
new file mode 100755
index 0000000000000000000000000000000000000000..f64faac454e52fe5e8fe9ce1fd3aa9afb57d33b3
--- /dev/null
+++ b/mojo/public/dart/third_party/csslib/bin/css.dart
@@ -0,0 +1,8 @@
+#!/usr/bin/env dart
+// Copyright (c) 2012, 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:csslib/css.dart' as css;
+
+void main(List<String> args) => css.main(args);