Revert "Remaining private libs"

sdk/lib/isolate/capability.dart

 // Copyright (c) 2014, 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:isolate";
+part of "isolate.dart";
 
 /**
  * An unforgeable object that comes back as equal when passed through other
  * isolates.
  *
  * Sending a capability object to another isolate, and getting it back,
  * will produce an object that is equal to the original.
  * There is no other way to create objects equal to a capability object.
  *
  * Capabilities can be used as access guards: A remote isolate can send
  * a request for an operation, but it is only allowed if the request contains
  * the correct capability object.
  *
  * This allows exposing the same interface to multiple clients,
  * but restricting some operations to only those clients
  * that have also been given the corresponding capability.
  *
  * Capabilities can be used inside a single isolate,
  * but they have no advantage over
  * just using `new Object` to create a unique object,
  * and it offers no real security against other code
  * running in the same isolate.
  */
 class Capability {
   /**
    * Create a new unforgeable capability object.
    */
   external factory Capability();
 }