Fix crash from ipc_fuzzer

chrome/browser/printing/print_view_manager_base.cc

Index: chrome/browser/printing/print_view_manager_base.cc
diff --git a/chrome/browser/printing/print_view_manager_base.cc b/chrome/browser/printing/print_view_manager_base.cc
index a13e643a67cec6ad83b1041ea6f4d79305c332e7..edc5aa6deafb237f1771bda5f952d41bf8c04fb2 100644
--- a/chrome/browser/printing/print_view_manager_base.cc
+++ b/chrome/browser/printing/print_view_manager_base.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/printing/print_view_manager_base.h"
 
+#include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/pref_service.h"
@@ -40,6 +41,18 @@ namespace printing {
 
 namespace {
 
+void ShowWarningMessageBox(const base::string16& message) {
+  // Runs always on the UI thread.
+  static bool is_dialog_shown = false;
+  if (is_dialog_shown)
+    return;
+  // Block opening dialog from nested task.
+  base::AutoReset<bool> auto_reset(&is_dialog_shown, true);
+
+  chrome::ShowMessageBox(nullptr, base::string16(), message,
+                         chrome::MESSAGE_BOX_TYPE_WARNING);
+}
+
 }  // namespace
 
 PrintViewManagerBase::PrintViewManagerBase(content::WebContents* web_contents)
@@ -195,11 +208,10 @@ void PrintViewManagerBase::OnPrintingFailed(int cookie) {
 }
 
 void PrintViewManagerBase::OnShowInvalidPrinterSettingsError() {
-  chrome::ShowMessageBox(NULL,
-                         base::string16(),
-                         l10n_util::GetStringUTF16(
-                             IDS_PRINT_INVALID_PRINTER_SETTINGS),
-                         chrome::MESSAGE_BOX_TYPE_WARNING);
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE, base::Bind(&ShowWarningMessageBox,
+                            l10n_util::GetStringUTF16(
+                                IDS_PRINT_INVALID_PRINTER_SETTINGS)));
 }
 
 void PrintViewManagerBase::DidStartLoading() {