Remove dart:platform library.

runtime/lib/platform_patch.dart

-// Copyright (c) 2013, 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.
-
-patch int get numberOfProcessors => _platform.numberOfProcessors;
-
-patch String get pathSeparator => _platform.pathSeparator;
-
-patch String get operatingSystem => _platform.operatingSystem;
-
-patch String get localHostname => _platform.localHostname;
-
-patch String get version => _platform.version;
-
-patch Map<String, String> get environment => _platform.environment;
-
-patch String get executable => _platform.executable;
-
-patch Uri get script => _platform.script;
-
-patch List<String> get executableArguments => _platform.executableArguments;
-
-patch String get packageRoot => _platform.packageRoot;
-
-class _Platform {
-  int get numberOfProcessors;
-  String get pathSeparator;
-  String get operatingSystem;
-  String get localHostname;
-  String get version;
-  Map get environment;
-  Uri get script;
-  String get executable;
-  List<String>  get executableArguments;
-  String get packageRoot;
-}
-
-// A non-default _Platform, with real values, is stored here by the embedder.
-_Platform _platform = new _DefaultPlatform();
-
-class _DefaultPlatform implements _Platform {
-  int get numberOfProcessors {
-    return null;
-  }
-
-  String get pathSeparator {
-    return null;
-  }
-
-  String get operatingSystem {
-    return null;
-  }
-
-  String get localHostname {
-    return null;
-  }
-
-  String get version {
-    return null;
-  }
-
-  Map get environment {
-    return null;
-  }
-
-  Uri get script {
-    return null;
-  }
-
-  String get executable {
-    return null;
-  }
-
-  List<String>  get executableArguments {
-    return new List<String>(0);
-  }
-
-  String get packageRoot {
-    return null;
-  }
-}