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

sdk/lib/convert/ascii.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.convert;
 
 /**
  * An instance of the default implementation of the [AsciiCodec].
  *
  * This instance provides a convenient access to the most common ASCII
  * use cases.
  *
  * Examples:
  *
  *     var encoded = ASCII.encode("This is ASCII!");
  *     var decoded = ASCII.decode([0x54, 0x68, 0x69, 0x73, 0x20, 0x69, 0x73,
  *                                 0x20, 0x41, 0x53, 0x43, 0x49, 0x49, 0x21]);
  */
 const ASCII = const AsciiCodec();
 
 const int _ASCII_MASK = 0x7F;
 
 /**
  * An [AsciiCodec] allows encoding strings as ASCII bytes
  * and decoding ASCII bytes to strings.
  */
-class AsciiCodec extends _Encoding {
+class AsciiCodec extends Encoding {
   final bool _allowInvalid;
   /**
    * Instantiates a new [AsciiCodec].
    *
    * If [allowInvalid] is true, the [decode] method and the converter
    * returned by [decoder] will default to allowing invalid values.
    * If allowing invalid values, the values will be decoded into the Unicode
    * Replacement character (U+FFFD). If not, an exception will be thrown.
    * Calls to the [decode] method can choose to override this default.
    *
    * Encoders will not accept invalid (non Latin-1) characters.
    */
   const AsciiCodec({bool allowInvalid: false}) : _allowInvalid = allowInvalid;
 
+  String get name => "us-ascii";
+
   /**
    * Decodes the ASCII [bytes] (a list of unsigned 7-bit integers) to the
    * corresponding string.
    *
    * If [bytes] contains values that are not in the range 0 .. 127, the decoder
    * will eventually throw a [FormatException].
    *
    * If [allowInvalid] is not provided, it defaults to the value used to create
    * this [AsciiCodec].
    */
@@ skipping 224 matching lines @@
         }
       }
     }
     if (start < end) {
       _utf8Sink.addSlice(source, start, end, isLast);
     } else if (isLast) {
       close();
     }
   }
 }