Revert "Remaining private libs"

sdk/lib/core/string_sink.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:core";
+part of "core.dart";
 
 abstract class StringSink {
   /**
    * Converts [obj] to a String by invoking [Object.toString] and 
    * adds the result to `this`.
    */
   void write(Object obj);
 
   /**
    * Iterates over the given [objects] and [write]s them in sequence.
    */
   void writeAll(Iterable objects, [String separator = ""]);
 
   /**
    * Converts [obj] to a String by invoking [Object.toString] and 
    * adds the result to `this`, followed by a newline.
    */
   void writeln([Object obj = ""]);
 
   /**
    * Writes the [charCode] to `this`.
    *
    * This method is equivalent to `write(new String.fromCharCode(charCode))`.
    */
   void writeCharCode(int charCode);
 }