Improve the encoding/decoding to/from system encoding on Windows

runtime/bin/utils_win.h

 // Copyright (c) 2012, 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.
 
 #ifndef BIN_UTILS_WIN_H_
 #define BIN_UTILS_WIN_H_
 
 #include "platform/globals.h"
 
 namespace dart {
 namespace bin {
 
 void FormatMessageIntoBuffer(DWORD code, wchar_t* buffer, int buffer_length);
 
+class StringUtilsWin {
+ public:
+  static char* WideToUtf8(wchar_t* wide,
+                          intptr_t len = -1,
+                          intptr_t* result_len = NULL);
+  static const char* WideToUtf8(const wchar_t* wide,
+                                intptr_t len = -1,
+                                intptr_t* result_len = NULL);
+  static wchar_t* Utf8ToWide(char* utf8,
+                             intptr_t len = -1,
+                             intptr_t* result_len = NULL);
+  static const wchar_t* Utf8ToWide(const char* utf8,
+                                   intptr_t len = -1,
+                                   intptr_t* result_len = NULL);
+};
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_UTILS_WIN_H_