[dart:io][windows] Make unicode characters display correctly.

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 601d4d7b7635f0031e63b320c2fa3a7b5bdf7526..bbbd8b7841ed8eb61e19d8d9d8f196d0d4b052e7 100644
--- a/runtime/bin/platform_win.cc
+++ b/runtime/bin/platform_win.cc
@@ -27,7 +27,12 @@ char* Platform::resolved_executable_name_ = NULL;
 int Platform::script_index_ = 1;
 char** Platform::argv_ = NULL;
 
+static int old_output_cp = -1;
+
 bool Platform::Initialize() {
+  ASSERT(old_output_cp == -1);
+  old_output_cp = GetConsoleOutputCP();
+  SetConsoleOutputCP(CP_UTF8);
   SetErrorMode(SEM_FAILCRITICALERRORS | SEM_NOOPENFILEERRORBOX);
   return true;
 }
@@ -124,6 +129,11 @@ const char* Platform::ResolveExecutablePath() {
 void Platform::Exit(int exit_code) {
   // TODO(zra): Remove once VM shuts down cleanly.
   ::dart::private_flag_windows_run_tls_destructors = false;
+  // Restore the console's output code page
+  if (old_output_cp != -1) {
+    SetConsoleOutputCP(old_output_cp);

[Florian Schneider, 2017/02/21 20:34:50]

Can there be multiple threads calling Platform::Exit? If yes, another thread
could have reset old_output_cp to -1 before this call here.

[zra, 2017/02/21 21:26:46]

Yes. This can happen if multiple isolates call Platform.exit() at the same time.
I've added a mutex to protect old_output_cp.

+    old_output_cp = -1;
+  }
   // On Windows we use ExitProcess so that threads can't clobber the exit_code.
   // See: https://code.google.com/p/nativeclient/issues/detail?id=2870
   ::ExitProcess(exit_code);