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

sdk/lib/async/zone.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.
 
-part of "dart:async";
+part of dart.async;
 
 typedef R ZoneCallback<R>();
 typedef R ZoneUnaryCallback<R, T>(T arg);
 typedef R ZoneBinaryCallback<R, T1, T2>(T1 arg1, T2 arg2);
 
 // TODO(floitsch): we are abusing generic typedefs as typedefs for generic
 // functions.
 /*ABUSE*/
 typedef R HandleUncaughtErrorHandler<R>(
     Zone self, ZoneDelegate parent, Zone zone, error, StackTrace stackTrace);
@@ skipping 1444 matching lines @@
         handleUncaughtError: errorHandler);
   }
   Zone zone = Zone.current
       .fork(specification: zoneSpecification, zoneValues: zoneValues);
   if (onError != null) {
     return zone.runGuarded(body);
   } else {
     return zone.run(body);
   }
 }