Fixes possible deadlock between history and bookmarks. The deadlock

chrome/browser/bookmarks/bookmark_model.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_BOOKMARKS_BOOKMARK_MODEL_H_
 #define CHROME_BROWSER_BOOKMARKS_BOOKMARK_MODEL_H_
 #pragma once
 
 #include <set>
 #include <vector>
@@ skipping 157 matching lines @@
 //
 // You should NOT directly create a BookmarkModel, instead go through the
 // Profile.
 class BookmarkModel : public NotificationObserver, public BookmarkService {
  public:
   explicit BookmarkModel(Profile* profile);
   virtual ~BookmarkModel();
 
   static void RegisterUserPrefs(PrefService* prefs);
 
+  // Invoked prior to destruction to release any necessary resources.
+  void Cleanup();
+
   // Loads the bookmarks. This is called by Profile upon creation of the
   // BookmarkModel. You need not invoke this directly.
   void Load();
 
   // Returns true if the model finished loading.
   // This is virtual so it can be mocked.
   virtual bool IsLoaded() const;
 
   // Returns the root node. The 'bookmark bar' node and 'other' node are
   // children of the root node.
@@ skipping 266 matching lines @@
   scoped_ptr<BookmarkIndex> index_;
 
   base::WaitableEvent loaded_signal_;
 
   scoped_ptr<BookmarkExpandedStateTracker> expanded_state_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(BookmarkModel);
 };
 
 #endif  // CHROME_BROWSER_BOOKMARKS_BOOKMARK_MODEL_H_