Implement redirect-stdout-on-close on Winows, to the 'NUL' device.

runtime/bin/eventhandler_win.cc

Index: runtime/bin/eventhandler_win.cc
diff --git a/runtime/bin/eventhandler_win.cc b/runtime/bin/eventhandler_win.cc
index 7c96ce88339311cd7978b0a451e2202a339880b3..f1257c3ce5054c900dbf047ba5ad14a4600be95e 100644
--- a/runtime/bin/eventhandler_win.cc
+++ b/runtime/bin/eventhandler_win.cc
@@ -11,6 +11,8 @@
 #include <winsock2.h>  // NOLINT
 #include <ws2tcpip.h>  // NOLINT
 #include <mswsock.h>  // NOLINT
+#include <io.h>  // NOLINT
+#include <fcntl.h>  // NOLINT
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
@@ -326,6 +328,18 @@ bool FileHandle::IsClosed() {
 }
 
 
+void FileHandle::DoClose() {
+  if (GetStdHandle(STD_OUTPUT_HANDLE) == handle_) {
+    int fd = _open("NUL", _O_WRONLY);
+    ASSERT(fd >= 0);
+    _dup2(fd, _fileno(stdout));
+    close(fd);
+  } else {
+    Handle::DoClose();
+  }
+}
+
+
 void SocketHandle::HandleIssueError() {
   int error = WSAGetLastError();
   if (error == WSAECONNRESET) {