Always mark stdout as blocking when using 'print'.

runtime/bin/platform_win.cc

 // 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.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "bin/platform.h"
 #include "bin/log.h"
 #include "bin/socket.h"
@@ skipping 46 matching lines @@
   FreeEnvironmentStringsW(strings);
   return result;
 }
 
 
 void Platform::FreeEnvironment(char** env, int count) {
   for (int i = 0; i < count; i++) free(env[i]);
   delete[] env;
 }
 
+
+void Platform::PrintBlocking(FILE* file, const char* format, ...) {
+  // No need to set blocking, as it's always blocking on Windows.
+  va_list args;
+  va_start(args, format);
+  vfprintf(file, format, args);
+  fflush(file);
+  va_end(args);
+}
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)