Improve syncing between dom distiller and the print preview request

chrome/browser/ui/webui/print_preview/print_preview_distiller.h

 // Copyright 2015 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_PRINT_PREVIEW_DISTILLER_H_
 #define CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_PRINT_PREVIEW_DISTILLER_H_
 
 #include "base/callback.h"
 #include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/values.h"
+#include "components/dom_distiller/core/task_tracker.h"
 #include "content/public/browser/web_contents_observer.h"
 
 namespace net {
 class URLRequestContextGetter;
 }
 
 // This class controls the rendering of the distilled contents
 // generated by a source web contents
 class PrintPreviewDistiller {
  public:
@@ skipping 20 matching lines @@
 
   content::WebContents* CreateWebContents(
       content::SessionStorageNamespace* session_storage_namespace,
       content::WebContents* source_web_contents);
 
   // The distilled rendered WebContents; may be null.
   scoped_ptr<content::WebContents> web_contents_;
 
   scoped_ptr<WebContentsDelegateImpl> web_contents_delegate_;
 
+  scoped_ptr<dom_distiller::ViewerHandle> viewer_handle_;
+
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewDistiller);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_PRINT_PREVIEW_DISTILLER_H_