Use ScopedNestedTaskAllower instead of background thread for print di…

…alog

Tasks need to be processed for painting to occur in other browser
windows while the modal dialog is up in Aura.

R=vitalybuka@chromium.org
BUG=342697,180997,343848

Review URL: https://codereview.chromium.org/164303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251373 0039d316-1c4b-4281-b951-d872f2087c98

printing/printing_context_win.cc

@@ -175,7 +175,6 @@ PrintingContextWin::~PrintingContextWin() {
   ReleaseContext();
 }
 
-// TODO(vitalybuka): Implement as ui::BaseShellDialog crbug.com/180997.
 void PrintingContextWin::AskUserForSettings(
     gfx::NativeView view, int max_pages, bool has_selection,
     const PrintSettingsCallback& callback) {
@@ -238,6 +237,14 @@ void PrintingContextWin::AskUserForSettings(
     dialog_options.Flags |= PD_NOPAGENUMS;
   }
 
+  // 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
+  // browser frame (but still being modal) so neither the browser frame nor
+  // the print dialog will get any input. See http://crbug.com/342697
+  // http://crbug.com/180997 for details.
+  base::MessageLoop::ScopedNestableTaskAllower allow(
+      base::MessageLoop::current());
   HRESULT hr = (*print_dialog_func_)(&dialog_options);
   if (hr != S_OK) {
     ResetSettings();

printing/printing_context_win_unittest.cc

@@ -10,6 +10,7 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/message_loop/message_loop.h"
 #include "printing/backend/printing_info_win.h"
 #include "printing/printing_test.h"
 #include "printing/printing_context.h"
@@ -159,6 +160,7 @@ TEST_F(PrintingContextTest, Base) {
 }
 
 TEST_F(PrintingContextTest, PrintAll) {
+  base::MessageLoop message_loop;
   if (IsTestCaseDisabled())
     return;