Block nested system print dialogs on Windows.

Browser needs to allow nested tasks to update backgroud tabs.
If rendered requests new system dialog, asan build crashes in COMDLG32.dll

NOTRY=true
BUG=451753

Review URL: https://codereview.chromium.org/934393003

Cr-Commit-Position: refs/heads/master@{#317611}

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

printing/printing_context_win.cc

@@ -359,7 +359,7 @@ PrintingContext::Result PrintingContextWin::InitializeSettings(
 
 HWND PrintingContextWin::GetRootWindow(gfx::NativeView view) {
   HWND window = NULL;
-  if (view)
+  if (view && view->GetHost())
     window = view->GetHost()->GetAcceleratedWidget();
   if (!window) {
     // TODO(maruel):  crbug.com/1214347 Get the right browser window instead.