Block nested system print dialogs on Windows

printing/printing_context_system_dialog_win.cc

Index: printing/printing_context_system_dialog_win.cc
diff --git a/printing/printing_context_system_dialog_win.cc b/printing/printing_context_system_dialog_win.cc
index 19fc42719ce990af1cd4abe16f25b0657aa3f8b8..b89f1a4e469ac89ca10b34942a95f8fd35a21010 100644
--- a/printing/printing_context_system_dialog_win.cc
+++ b/printing/printing_context_system_dialog_win.cc
@@ -4,6 +4,7 @@
 
 #include "printing/printing_context_system_dialog_win.h"
 
+#include "base/auto_reset.h"
 #include "base/message_loop/message_loop.h"
 #include "printing/backend/win_helper.h"
 #include "printing/print_settings_initializer_win.h"
@@ -84,6 +85,13 @@ void PrintingContextSytemDialogWin::Cancel() {
 }
 
 HRESULT PrintingContextSytemDialogWin::ShowPrintDialog(PRINTDLGEX* options) {
+  // Runs always on the UI thread.
+  static bool is_dialog_shown = false;
+  if (is_dialog_shown)
+    return E_FAIL;
+  // Block opening dialog from nested task. It crashes PrintDlgEx.
+  base::AutoReset<bool> auto_reset(&is_dialog_shown, true);
+
   // Note that this cannot use ui::BaseShellDialog as the print dialog is
   // system modal: opening it from a background thread can cause Windows to
   // get the wrong Z-order which will make the print dialog appear behind the