[Extensions] Don't remove the bookmark drag event router as delegate

chrome/browser/extensions/api/bookmark_manager_private/bookmark_manager_private_api.cc

 // 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.
 
 #include "chrome/browser/extensions/api/bookmark_manager_private/bookmark_manager_private_api.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 273 matching lines @@
   event_router_.reset(new BookmarkManagerPrivateEventRouter(
       browser_context_,
       BookmarkModelFactory::GetForBrowserContext(browser_context_)));
 }
 
 BookmarkManagerPrivateDragEventRouter::BookmarkManagerPrivateDragEventRouter(
     content::WebContents* web_contents)
     : web_contents_(web_contents),
       profile_(
           Profile::FromBrowserContext(web_contents_->GetBrowserContext())) {
+  // We need to guarantee the BookmarkTabHelper is created.
+  BookmarkTabHelper::CreateForWebContents(web_contents_);
   BookmarkTabHelper* bookmark_tab_helper =
       BookmarkTabHelper::FromWebContents(web_contents_);
   bookmark_tab_helper->set_bookmark_drag_delegate(this);
 }
 
 BookmarkManagerPrivateDragEventRouter::
     ~BookmarkManagerPrivateDragEventRouter() {
-  BookmarkTabHelper* bookmark_tab_helper =
-      BookmarkTabHelper::FromWebContents(web_contents_);
-  if (bookmark_tab_helper->bookmark_drag_delegate() == this)
-    bookmark_tab_helper->set_bookmark_drag_delegate(NULL);
+  // No need to remove ourselves as the BookmarkTabHelper's delegate, since they
+  // are both WebContentsUserData and will be deleted at the same time.
 }
 
 void BookmarkManagerPrivateDragEventRouter::MaybeCreateForWebContents(
     content::WebContents* web_contents) {
   content::BrowserContext* context = web_contents->GetBrowserContext();
   const Extension* extension =
       ExtensionRegistry::Get(context)
           ->enabled_extensions()
           .GetExtensionOrAppByURL(
               web_contents->GetSiteInstance()->GetSiteURL());
@@ skipping 557 matching lines @@
 
   RedoInfo::Results::Result result;
   result.enabled = undo_manager->redo_count() > 0;
   result.label = base::UTF16ToUTF8(undo_manager->GetRedoLabel());
 
   results_ = RedoInfo::Results::Create(result);
   return true;
 }
 
 }  // namespace extensions