Remove Encoding-enum from dart:io and add interface in dart:convert.

sdk/lib/io/io_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.io;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by all [StringSink] methods and will delay
  * a [addStream] until the buffer is flushed.
  *
  * When the [IOSink] is bound to a stream (through [addStream]) any call
  * to the [IOSink] will throw a [StateError]. When the [addStream] completes,
  * the [IOSink] will again be open for all calls.
  *
  * If data is added to the [IOSink] after the sink is closed, the data will be
  * ignored. Use the [done] future to be notified when the [IOSink] is closed.
  */
 abstract class IOSink implements StreamSink<List<int>>, StringSink {
   factory IOSink(StreamConsumer<List<int>> target,
-                 {Encoding encoding: Encoding.UTF_8})
+                 {Encoding encoding: UTF8})
       => new _IOSinkImpl(target, encoding);
 
   /**
    * The [Encoding] used when writing strings. Depending on the
    * underlying consumer this property might be mutable.
    */
   Encoding encoding;
 
   /**
    * Writes the bytes uninterpreted to the consumer. While the call is
@@ skipping 164 matching lines @@
     String string;
     if (obj is String) {
       string = obj;
     } else {
       string = obj.toString();
       if (string is! String) {
         throw new ArgumentError('toString() did not return a string');
       }
     }
     if (string.isEmpty) return;
-    add(_encodeString(string, _encoding));
+    add(_encoding.encode(string));
   }
 
   void writeAll(Iterable objects, [String separator = ""]) {
     Iterator iterator = objects.iterator;
     if (!iterator.moveNext()) return;
     if (separator.isEmpty) {
       do {
         write(iterator.current);
       } while (iterator.moveNext());
     } else {
       write(iterator.current);
       while (iterator.moveNext()) {
         write(separator);
         write(iterator.current);
       }
     }
   }
 
   void writeln([Object obj = ""]) {
     write(obj);
     write("\n");
   }
 
   void writeCharCode(int charCode) {
     write(new String.fromCharCode(charCode));
   }
 }