Cancel the pending print preview request when the user request to show the system dialog.

chrome/browser/ui/webui/print_preview_ui.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_UI_WEBUI_PRINT_PREVIEW_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_UI_H_
 #pragma once
 
 #include <string>
 
@@ skipping 78 matching lines @@
   // Notifies the Web UI that initiator tab is closed, so we can disable all the
   // controls that need the initiator tab for generating the preview data.
   void OnInitiatorTabClosed();
 
   // Notifies the Web UI that the initiator tab has crashed.
   void OnInitiatorTabCrashed();
 
   // Notifies the Web UI renderer that file selection has been cancelled.
   void OnFileSelectionCancelled();
 
+  // Notifies the Web UI to cancel the pending preview request.
+  void OnCancelPendingPreviewRequest();
+
  private:
   FRIEND_TEST_ALL_PREFIXES(PrintPreviewTabControllerUnitTest,
                            TitleAfterReload);
 
   // Returns the Singleton instance of the PrintPreviewDataService.
   PrintPreviewDataService* print_preview_data_service();
 
   base::TimeTicks initial_preview_start_time_;
 
   // Store the PrintPreviewUI address string.
   std::string preview_ui_addr_str_;
 
   // Weak pointer to the WebUI handler.
   PrintPreviewHandler* handler_;
 
   // Store the |initiator_url| in order to display an accurate error message
   // when the initiator tab is closed/crashed.
   std::string initiator_url_;
 
   // Store the initiator tab title, used for populating the print preview tab
   // title.
   string16 initiator_tab_title_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_UI_H_