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

sdk/lib/io/websocket_impl.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;
 
 const String _webSocketGUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
 
 class _WebSocketMessageType {
   static const int NONE = 0;
@@ skipping 445 matching lines @@
     }
     if (message is _WebSocketPing) {
       addFrame(_WebSocketOpcode.PING, message.payload, sink);
       return;
     }
     List<int> data;
     int opcode;
     if (message != null) {
       if (message is String) {
         opcode = _WebSocketOpcode.TEXT;
-        data = _encodeString(message);
+        data = UTF8.encode(message);
       } else {
         if (message is !List<int>) {
           throw new ArgumentError(message);
         }
         opcode = _WebSocketOpcode.BINARY;
         data = message;
       }
     } else {
       opcode = _WebSocketOpcode.TEXT;
     }
     addFrame(opcode, data, sink);
   }
 
   void handleDone(EventSink<List<int>> sink) {
     int code = webSocket._outCloseCode;
     String reason = webSocket._outCloseReason;
     List<int> data;
     if (code != null) {
       data = new List<int>();
       data.add((code >> 8) & 0xFF);
       data.add(code & 0xFF);
       if (reason != null) {
-        data.addAll(_encodeString(reason));
+        data.addAll(UTF8.encode(reason));
       }
     }
     addFrame(_WebSocketOpcode.CLOSE, data, sink);
     sink.close();
   }
 
   void addFrame(int opcode, List<int> data, EventSink<List<int>> sink) {
     createFrame(opcode, data, webSocket._serverSide).forEach(sink.add);
   }
 
@@ skipping 374 matching lines @@
            (code < WebSocketStatus.NORMAL_CLOSURE ||
             code == WebSocketStatus.RESERVED_1004 ||
             code == WebSocketStatus.NO_STATUS_RECEIVED ||
             code == WebSocketStatus.ABNORMAL_CLOSURE ||
             (code > WebSocketStatus.INTERNAL_SERVER_ERROR &&
              code < WebSocketStatus.RESERVED_1015) ||
             (code >= WebSocketStatus.RESERVED_1015 &&
              code < 3000));
   }
 }