PrintPreview: Preview generation should not block print button.

chrome/browser/printing/background_printing_manager.cc

 // Copyright (c) 2011 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/background_printing_manager.h"
 
 #include "chrome/browser/printing/print_job.h"
 #include "chrome/browser/printing/print_preview_tab_controller.h"
 #include "chrome/browser/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/browser_list.h"
@@ skipping 80 matching lines @@
 std::set<TabContentsWrapper*>::const_iterator
     BackgroundPrintingManager::begin() {
   return printing_contents_.begin();
 }
 
 std::set<TabContentsWrapper*>::const_iterator
     BackgroundPrintingManager::end() {
   return printing_contents_.end();
 }
 
+bool BackgroundPrintingManager::HasTabContents(TabContentsWrapper* entry) {
+  return printing_contents_.find(entry) != printing_contents_.end();
+}
+
 }  // namespace printing