Print Preview: Make preview generation event driven to eliminate synchronous messages.

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 18 matching lines @@
 
   // Sets the print preview |data|.
   void SetPrintPreviewData(const RefCountedBytes* data);
 
   // Notify the Web UI that there is a print preview request.
   // There should be a matching call to OnPreviewDataIsAvailable() or
   // OnPrintPreviewFailed().
   void OnPrintPreviewRequest();
 
   // Notify the Web UI that the print preview will have |page_count| pages.
-  void OnDidGetPreviewPageCount(int page_count);
+  void OnDidGetPreviewPageCount(int document_cookie_, int page_count);
 
   // Notify the Web UI that the 0-based page |page_number| has been rendered.
   void OnDidPreviewPage(int page_number);
 
   // Notify the Web UI renderer that preview data is available.
   // |expected_pages_count| specifies the total number of pages.
   // |job_title| is the title of the page being previewed.
   // |modifiable| indicates if the preview can be rerendered with different
   // print settings.
   // |preview_request_id| indicates wich request resulted in this response.
@@ skipping 18 matching lines @@
   // |initiator_tab_url| is passed in order to display a more accurate error
   // message.
   void OnInitiatorTabClosed(const std::string& initiator_tab_url);
 
   // Notify the Web UI renderer that file selection has been cancelled.
   void OnFileSelectionCancelled();
 
   // Return true if there are pending requests.
   bool HasPendingRequests();
 
+  int document_cookie();
+
  private:
   // Helper function
   PrintPreviewDataService* print_preview_data_service();
 
   void DecrementRequestCount();
 
   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_;
 
   // The number of print preview requests in flight.
   uint32 request_count_;
 
+  // Document cookie from the initiator renderer.
+  int document_cookie_;
+
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_UI_H_