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

runtime/bin/platform_win.cc

Index: runtime/bin/platform_win.cc
diff --git a/runtime/bin/platform_win.cc b/runtime/bin/platform_win.cc
index d109c82dda07cbddb8cca9596a8322fda756268f..9830db2c9ebc863856023aca91260b7105a7d650 100644
--- a/runtime/bin/platform_win.cc
+++ b/runtime/bin/platform_win.cc
@@ -10,6 +10,7 @@
 #include "bin/log.h"
 #include "bin/socket.h"
 #include "bin/utils.h"
+#include "bin/utils_win.h"
 
 
 namespace dart {
@@ -66,7 +67,7 @@ char** Platform::Environment(intptr_t* count) {
   tmp = strings;
   for (intptr_t current = 0; current < i;) {
     // Skip the strings that were not counted above.
-    if (*tmp != '=') result[current++] = StringUtils::WideToUtf8(tmp);
+    if (*tmp != '=') result[current++] = StringUtilsWin::WideToUtf8(tmp);
     tmp += (wcslen(tmp) + 1);
   }
   FreeEnvironmentStringsW(strings);
@@ -96,7 +97,7 @@ char* Platform::ResolveExecutablePath() {
     free(tmp_buffer);
     return NULL;
   }
-  char* path = StringUtils::WideToUtf8(tmp_buffer);
+  char* path = StringUtilsWin::WideToUtf8(tmp_buffer);
   free(tmp_buffer);
   // Return the canonical path as the returned path might contain symlinks.
   char* canon_path = File::GetCanonicalPath(path);