Merge pull request #2444 from abarth/rrect_license

Add a license header to RRect.dart

sky/engine/core/painting/RRect.dart

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
 part of dart_ui;
 
 // A rounded rectangle with the same radii for all four corners.