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

runtime/bin/utils_win.h

Index: runtime/bin/utils_win.h
diff --git a/runtime/bin/utils_win.h b/runtime/bin/utils_win.h
index a0447604cfee6d5545a40139e2226e2ef86fda9a..92de84e661403c5ffa7478d35dcab5e18a3e72a4 100644
--- a/runtime/bin/utils_win.h
+++ b/runtime/bin/utils_win.h
@@ -12,6 +12,22 @@ 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