Get rid of all the library tags.

lib/src/backend/operating_system.dart

 // Copyright (c) 2015, 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.
 
-library test.backend.operating_system;
-
 /// An enum of all operating systems supported by Dart.
 ///
 /// This is used for selecting which operating systems a test can run on. Even
 /// for browser tests, this indicates the operating system of the machine
 /// running the test runner.
 class OperatingSystem {
   /// Microsoft Windows.
   static const windows = const OperatingSystem._("windows");
 
   /// Mac OS X.
@@ skipping 40 matching lines @@
   /// The name of the operating system.
   final String name;
 
   /// Whether this is a POSIX-ish operating system.
   bool get isPosix => this != windows && this != none;
 
   const OperatingSystem._(this.name);
 
   String toString() => name;
 }