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

sdk/lib/async/stream_pipe.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;
 
 /** Runs user code and takes actions depending on success or failure. */
 _runUserCode<T>(
     T userCode(), onSuccess(T value), onError(error, StackTrace stackTrace)) {
   try {
     onSuccess(userCode());
   } catch (e, s) {
     AsyncError replacement = Zone.current.errorCallback(e, s);
     if (replacement == null) {
       onError(e, s);
@@ skipping 460 matching lines @@
         _addErrorWithReplacement(sink, e, s);
         return null;
       }
       if (!isEqual) {
         sink._add(inputEvent);
         _previous = inputEvent;
       }
     }
   }
 }