PrintPreview: Preview generation should not block print button.

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 26 matching lines @@
   void OnPreviewDataIsAvailable(int expected_pages_count,
                                 const string16& job_title,
                                 bool modifiable);
 
   // Notify 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.
   // |initiator_tab_url| is passed in order to display a more accurate error
   // message.
   void OnInitiatorTabClosed(const std::string& initiator_tab_url);
 
+  void setTabHiddenForPrint() {
+    is_tab_hidden_for_print_ = true;
+  }
+
+  // Returns true if the current tab is hidden for printing.
+  bool isHidden() {
+    return is_tab_hidden_for_print_;
+  }
+
  private:
   // Helper function
   PrintPreviewDataService* print_preview_data_service();
 
   base::TimeTicks initial_preview_start_time_;
 
   // Store the PrintPreviewUI address string.
   std::string preview_ui_addr_str_;
 
+  // True when the current tab is hidden for printing.
+  bool is_tab_hidden_for_print_;
+
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_UI_H_