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

sdk/lib/convert/latin1.dart

Index: sdk/lib/convert/latin1.dart
diff --git a/sdk/lib/convert/latin1.dart b/sdk/lib/convert/latin1.dart
index 3e9232f942b0a7e41dad871cadc07fbfa2cf8dd4..2fca67cc64f34f01568d3b4e993654d0cc0144ce 100644
--- a/sdk/lib/convert/latin1.dart
+++ b/sdk/lib/convert/latin1.dart
@@ -24,7 +24,7 @@ const int _LATIN1_MASK = 0xFF;
  * A [LatinCodec] encodes strings to ISO Latin-1 (aka ISO-8859-1) bytes
  * and decodes Latin-1 bytes to strings.
  */
-class Latin1Codec extends _Encoding {
+class Latin1Codec extends Encoding {
   final bool _allowInvalid;
   /**
    * Instantiates a new [Latin1Codec].
@@ -38,6 +38,8 @@ class Latin1Codec extends _Encoding {
    */
   const Latin1Codec({bool allowInvalid: false}) : _allowInvalid = allowInvalid;
 
+  String get name => "iso-8859-1";
+
   /**
    * Decodes the Latin-1 [bytes] (a list of unsigned 8-bit integers) to the
    * corresponding string.