Reland fix for thumbnail generation.

chrome/browser/thumbnails/thumbnail_tab_helper.h

Index: chrome/browser/thumbnails/thumbnail_tab_helper.h
diff --git a/chrome/browser/thumbnails/thumbnail_tab_helper.h b/chrome/browser/thumbnails/thumbnail_tab_helper.h
index ae13bbb73d2b44bc5b38f8d808c7c83c6376902f..9e95b462b56639081de4908dd40d577828f6f75d 100644
--- a/chrome/browser/thumbnails/thumbnail_tab_helper.h
+++ b/chrome/browser/thumbnails/thumbnail_tab_helper.h
@@ -6,6 +6,7 @@
 #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"
@@ -25,6 +26,8 @@ class ThumbnailTabHelper
  public:
   ~ThumbnailTabHelper() override;
 
+  void set_thumbnail_generation_in_progress(bool flag);
+
  private:
   explicit ThumbnailTabHelper(content::WebContents* contents);
   friend class content::WebContentsUserData<ThumbnailTabHelper>;
@@ -51,6 +54,9 @@ class ThumbnailTabHelper
   content::NotificationRegistrar registrar_;
 
   bool load_interrupted_;
+  bool thumbnail_generation_in_progress_;
+
+  base::WeakPtrFactory<ThumbnailTabHelper> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailTabHelper);
 };