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

runtime/bin/process_patch.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.
 
 patch class _WindowsCodePageDecoder {
   /* patch */ static String _decodeBytes(List<int> bytes)
       native "SystemEncodingToString";
 }
 
 
@@ skipping 20 matching lines @@
     return process._start();
   }
 
   /* patch */ static Future<ProcessResult> run(
       String executable,
       List<String> arguments,
       {String workingDirectory,
        Map<String, String> environment,
        bool includeParentEnvironment: true,
        bool runInShell: false,
-       Encoding stdoutEncoding: Encoding.SYSTEM,
-       Encoding stderrEncoding: Encoding.SYSTEM}) {
+       Encoding stdoutEncoding: SYSTEM_ENCODING,
+       Encoding stderrEncoding: SYSTEM_ENCODING}) {
     return _runNonInteractiveProcess(executable,
                                      arguments,
                                      workingDirectory,
                                      environment,
                                      includeParentEnvironment,
                                      runInShell,
                                      stdoutEncoding,
                                      stderrEncoding);
   }
 
   /* patch */ static ProcessResult runSync(
       String executable,
       List<String> arguments,
       {String workingDirectory,
        Map<String, String> environment,
        bool includeParentEnvironment: true,
        bool runInShell: false,
-       Encoding stdoutEncoding: Encoding.SYSTEM,
-       Encoding stderrEncoding: Encoding.SYSTEM}) {
+       Encoding stdoutEncoding: SYSTEM_ENCODING,
+       Encoding stderrEncoding: SYSTEM_ENCODING}) {
     return _runNonInteractiveProcessSync(executable,
                                          arguments,
                                          workingDirectory,
                                          environment,
                                          includeParentEnvironment,
                                          runInShell,
                                          stdoutEncoding,
                                          stderrEncoding);
   }
 }
@@ skipping 245 matching lines @@
     }
 
     var result = _wait(
         _stdin._sink._nativeSocket,
         _stdout._stream._nativeSocket,
         _stderr._stream._nativeSocket,
         _exitHandler._nativeSocket);
 
     getOutput(output, encoding) {
       if (stderrEncoding == null) return output;
-      return _decodeString(output, encoding);
+      return encoding.decode(output);
     }
 
     return new _ProcessResult(
         result[0],
         result[1],
         getOutput(result[2], stdoutEncoding),
         getOutput(result[3], stderrEncoding));
   }
 
   bool _startNative(String path,
@@ skipping 79 matching lines @@
     p.stdin.close();
 
     // Setup stdout and stderr handling.
     Future foldStream(Stream<List<int>> stream, Encoding encoding) {
       if (encoding == null) {
         return stream
             .fold(new BytesBuilder(), (builder, data) => builder..add(data))
             .then((builder) => builder.takeBytes());
       } else {
         return stream
-            .transform(new StringDecoder(encoding))
+            .transform(encoding.decoder)
             .fold(
                 new StringBuffer(),
                 (buf, data) {
                   buf.write(data);
                   return buf;
                 })
             .then((sb) => sb.toString());
       }
     }
 
@@ skipping 29 matching lines @@
   const _ProcessResult(int this.pid,
                        int this.exitCode,
                        this.stdout,
                        this.stderr);
 
   final int pid;
   final int exitCode;
   final stdout;
   final stderr;
 }