Add a missing copyright notice.

pkg/front_end/lib/src/base/library_info.dart

+// Copyright (c) 2017, 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.
+
 /// A bit flag used by [LibraryInfo] indicating that a library is used by
 /// dart2js.
 ///
 /// This declaration duplicates the declaration in the SDK's "libraries.dart".
 const int DART2JS_PLATFORM = 1;
 
 /// A bit flag used by [LibraryInfo] indicating that a library is used by the
 /// VM.
 ///
 /// This declaration duplicates the declaration in the SDK's "libraries.dart".
@@ skipping 135 matching lines @@
   final int level;
 
   final String name;
 
   final String description;
 
   const Maturity(this.level, this.name, this.description);
 
   String toString() => "$name: $level\n$description\n";
 }