PrintPreview: Preview generation should not block print button.

chrome/browser/printing/background_printing_manager.h

 // 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.
 
 #ifndef CHROME_BROWSER_PRINTING_BACKGROUND_PRINTING_MANAGER_H_
 #define CHROME_BROWSER_PRINTING_BACKGROUND_PRINTING_MANAGER_H_
 #pragma once
 
 #include <set>
 
@@ skipping 18 matching lines @@
 
   // Takes ownership of |content| and deletes it when |content| finishes
   // printing. This removes the TabContentsWrapper from its TabStrip and
   // hides it from the user.
   void OwnTabContents(TabContentsWrapper* content);
 
   // Let others iterate over the list of background printing tabs.
   std::set<TabContentsWrapper*>::const_iterator begin();
   std::set<TabContentsWrapper*>::const_iterator end();
 
+  // Returns true if |printing_contents_| contains |entry|.
+  bool HasTabContents(TabContentsWrapper* entry);
+
   // NotificationObserver overrides:
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,
                        const NotificationDetails& details) OVERRIDE;
 
  private:
   // The set of tabs managed by BackgroundPrintingManager.
   std::set<TabContentsWrapper*> printing_contents_;
 
   NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundPrintingManager);
 };
 
 }  // namespace printing
 
 #endif  // CHROME_BROWSER_PRINTING_BACKGROUND_PRINTING_MANAGER_H_