Print preview: Display a dummy page when a user visits chrome://print directly.

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 149 matching lines @@
   // Indicates whether the source document can be modified.
   bool source_is_modifiable_;
 
   // Store the initiator tab title, used for populating the print preview tab
   // title.
   string16 initiator_tab_title_;
 
   // Keeps track of whether OnClosePrintPreviewTab() has been called or not.
   bool tab_closed_;
 
+  // True if the user visited the page directly, false if it's a live UI.
+  bool is_dummy_;
+
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_UI_H_