Revert "Change some platform libraries to use `part of URI`."

sdk/lib/async/future_impl.dart

 // Copyright (c) 2012, 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.
 
-part of "dart:async";
+part of dart.async;
 
 /** The onValue and onError handlers return either a value or a future */
 typedef FutureOr<T> _FutureOnValue<S, T>(S value);
 /** Test used by [Future.catchError] to handle skip some errors. */
 typedef bool _FutureErrorTest(Object error);
 /** Used by [WhenFuture]. */
 typedef dynamic _FutureAction();
 
 abstract class _Completer<T> implements Completer<T> {
   final _Future<T> future = new _Future<T>();
@@ skipping 719 matching lines @@
       }
     }, onError: (e, s) {
       if (timer.isActive) {
         timer.cancel();
         result._completeError(e, s);
       }
     });
     return result;
   }
 }