Added missing copyright

Author: mvanbeusekom

packages/cross_file/lib/cross_file.dart

@@ -1 +1,5 @@
+// Copyright 2018 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.
+
 export 'src/cross_file.dart';

packages/cross_file/lib/src/cross_file.dart

@@ -1,3 +1,7 @@
+// Copyright 2018 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.
+
 export 'types/interface.dart'
     if (dart.library.html) 'types/html.dart'
     if (dart.library.io) 'types/io.dart';

packages/cross_file/lib/src/types/base.dart

@@ -1,3 +1,7 @@
+// Copyright 2018 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.
+
 import 'dart:convert';
 import 'dart:typed_data';
 

packages/cross_file/lib/src/types/html.dart

@@ -1,3 +1,7 @@
+// Copyright 2018 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.
+
 import 'dart:convert';
 import 'dart:typed_data';
 

packages/cross_file/lib/src/types/interface.dart

@@ -1,3 +1,7 @@
+// Copyright 2018 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.
+
 import 'dart:typed_data';
 import 'package:meta/meta.dart';
 

packages/cross_file/lib/src/types/io.dart

@@ -1,3 +1,7 @@
+// Copyright 2018 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.
+
 import 'dart:convert';
 import 'dart:io';
 import 'dart:typed_data';

packages/cross_file/lib/src/web_helpers/web_helpers.dart

@@ -1,3 +1,7 @@
+// Copyright 2018 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.
+
 import 'dart:html';
 
 /// Create anchor element with download attribute