Reapply change to use system code page on Windows to fix Pub.

runtime/bin/process_patch.dart

Index: runtime/bin/process_patch.dart
diff --git a/runtime/bin/process_patch.dart b/runtime/bin/process_patch.dart
index 4cdc85333ae9c0cf21325d3eaeeca963bab520d6..6646d07a18a6ca70f4e6e01b94323394c03ca4bd 100644
--- a/runtime/bin/process_patch.dart
+++ b/runtime/bin/process_patch.dart
@@ -2,6 +2,18 @@
 // 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";
+}
+
+
+patch class _WindowsCodePageEncoder {
+  /* patch */ static List<int> _encodeString(String string)
+      native "StringToSystemEncoding";
+}
+
+
 patch class Process {
   /* patch */ static Future<Process> start(String executable,
                                            List<String> arguments,
@@ -278,8 +290,8 @@ class _NonInteractiveProcess {
                          ProcessOptions options) {
     _completer = new Completer<ProcessResult>();
     // Extract output encoding options and verify arguments.
-    var stdoutEncoding = Encoding.UTF_8;
-    var stderrEncoding = Encoding.UTF_8;
+    var stdoutEncoding = Encoding.SYSTEM;
+    var stderrEncoding = Encoding.SYSTEM;
     if (options != null) {
       if (options.stdoutEncoding != null) {
         stdoutEncoding = options.stdoutEncoding;