Reland fix for thumbnail generation.

chrome/browser/thumbnails/thumbnail_tab_helper.h

 // Copyright (c) 2012 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_THUMBNAILS_THUMBNAIL_TAB_HELPER_H_
 #define CHROME_BROWSER_THUMBNAILS_THUMBNAIL_TAB_HELPER_H_
 
 #include "base/basictypes.h"
+#include "base/memory/weak_ptr.h"
 #include "chrome/browser/thumbnails/thumbnailing_context.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/readback_types.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 namespace content {
 class RenderViewHost;
 class RenderWidgetHost;
 }
 
 class ThumbnailTabHelper
     : public content::NotificationObserver,
       public content::WebContentsObserver,
       public content::WebContentsUserData<ThumbnailTabHelper> {
  public:
   ~ThumbnailTabHelper() override;
 
+  void set_thumbnail_generation_in_progress(bool flag);
+
  private:
   explicit ThumbnailTabHelper(content::WebContents* contents);
   friend class content::WebContentsUserData<ThumbnailTabHelper>;
 
   // content::NotificationObserver overrides.
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // content::WebContentsObserver overrides.
   void RenderViewDeleted(content::RenderViewHost* render_view_host) override;
   void DidStartLoading() override;
   void NavigationStopped() override;
 
   // Update the thumbnail of the given tab contents if necessary.
   void UpdateThumbnailIfNecessary(content::WebContents* web_contents);
 
   // Called when a render view host was created for a WebContents.
   void RenderViewHostCreated(content::RenderViewHost* renderer);
 
   // Indicates that the given widget has changed is visibility.
   void WidgetHidden(content::RenderWidgetHost* widget);
 
   content::NotificationRegistrar registrar_;
 
   bool load_interrupted_;
+  bool thumbnail_generation_in_progress_;
+
+  base::WeakPtrFactory<ThumbnailTabHelper> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailTabHelper);
 };
 
 #endif  // CHROME_BROWSER_THUMBNAILS_THUMBNAIL_TAB_HELPER_H_