Make the PrintDlgEx() call in the UI thread.

chrome/browser/printing/print_job_worker.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/printing/print_job_worker.h"
 
 #include "base/message_loop.h"
 #include "chrome/browser/printing/print_job.h"
 #include "chrome/browser/printing/printed_document.h"
 #include "chrome/browser/printing/printed_page.h"
@@ skipping 49 matching lines @@
 }
 
 void PrintJobWorker::SetNewOwner(PrintJobWorkerOwner* new_owner) {
   DCHECK(page_number_ == PageNumber::npos());
   owner_ = new_owner;
 }
 
 void PrintJobWorker::GetSettings(bool ask_user_for_settings,
                                  HWND parent_window,
                                  int document_page_count) {
-  DCHECK_EQ(message_loop(), MessageLoop::current());
+  if (ask_user_for_settings) {
+    // No way to retrieve the ui (browser) message loop.
+    // DCHECK_EQ(ui_message_loop_, MessageLoop::current());
+  } else {
+    DCHECK_EQ(message_loop(), MessageLoop::current());
+  }
   DCHECK_EQ(page_number_, PageNumber::npos());
 
   // Recursive task processing is needed for the dialog in case it needs to be
   // destroyed by a task.
   MessageLoop::current()->SetNestableTasksAllowed(true);
 
   PrintingContext::Result result;
   if (ask_user_for_settings) {
     result = printing_context_.AskUserForSettings(parent_window,
                                                   document_page_count);
@@ skipping 211 matching lines @@
     printing::PrintJobWorker* obj) {
   DCHECK(!owner_.get());
   owner_ = obj->owner_;
 }
 
 void RunnableMethodTraits<printing::PrintJobWorker>::ReleaseCallee(
     printing::PrintJobWorker* obj) {
   DCHECK_EQ(owner_, obj->owner_);
   owner_ = NULL;
 }