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

sdk/lib/io/process.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;
 
 // TODO(ager): The only reason for this class is that we
 // cannot patch a top-level at this point.
 class _ProcessUtils {
   external static void _exit(int status);
@@ skipping 111 matching lines @@
    * If [includeParentEnvironment] is `true`, the process's environment will
    * include the parent process's environment, with [environment] taking
    * precedence. Default is `true`.
    *
    * If [runInShell] is true, the process will be spawned through a system
    * shell. On Linux and Mac OS, `/bin/sh` is used, while
    * `%WINDIR%\system32\cmd.exe` is used on Windows.
    *
    * The encoding used for decoding `stdout` and `stderr` into text is
    * controlled through [stdoutEncoding] and [stderrEncoding]. The
-   * default encoding is `Encoding.SYSTEM`. If `null` is used no
+   * default encoding is [SYSTEM_ENCODING]. If `null` is used no
    * decoding will happen and the [ProcessResult] will hold binary
    * data.
    *
    * Returns a `Future<ProcessResult>` that completes with the
    * result of running the process, i.e., exit code, standard out and
    * standard in.
    */
   external 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});
 
 
   /**
    * Starts a process and runs it to completion. This is a synchronous
    * call and will block until the child process terminates.
    *
    * The arguments are the same as for `Process.run`.
    *
    * Returns a `ProcessResult` with the result of running the process,
    * i.e., exit code, standard out and standard in.
    */
   external 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});
 
   /**
    * Returns the standard output stream of the process as a [:Stream:].
    *
    * Throws an [UnsupportedError] if the process is
    * non-interactive.
    */
   Stream<List<int>> get stdout;
 
   /**
@@ skipping 139 matching lines @@
   /**
    * Contains the system message for the process exception if any.
    */
   final String message;
 
   /**
    * Contains the OS error code for the process exception if any.
    */
   final int errorCode;
 }