Print preview page selection should not require a rerendering of draft pages.

chrome/browser/printing/print_preview_data_service.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_PRINT_PREVIEW_DATA_SERVICE_H_
 #define CHROME_BROWSER_PRINTING_PRINT_PREVIEW_DATA_SERVICE_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 22 matching lines @@
   // or |printing::COMPLETE_PREVIEW_DOCUMENT_INDEX| to represent complete
   // preview data. Use |index| to set/update a specific preview page data.
   // NOTE: PrintPreviewDataStore owns the data. Do not refcount |data| before
   // calling this function. It will be refcounted in PrintPreviewDataStore.
   void SetDataEntry(const std::string& preview_ui_addr_str, int index,
                     const RefCountedBytes* data);
 
   // Remove the corresponding PrintPreviewUI entry from the map.
   void RemoveEntry(const std::string& preview_ui_addr_str);
 
+  // Returns the available draft page count.
+  int GetAvailableDraftPageCount(const std::string& preview_ui_addr_str);
+
  private:
   friend struct DefaultSingletonTraits<PrintPreviewDataService>;
 
   // 1:1 relationship between PrintPreviewUI and data store object.
   // Key: Print preview UI address string.
   // Value: Print preview data store object.
   typedef std::map<std::string, scoped_refptr<PrintPreviewDataStore> >
       PreviewDataStoreMap;
 
   PrintPreviewDataService();
   virtual ~PrintPreviewDataService();
 
   PreviewDataStoreMap data_store_map_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewDataService);
 };
 
 #endif  // CHROME_BROWSER_PRINTING_PRINT_PREVIEW_DATA_SERVICE_H_