bookmarks: Forward declare some classes in header files when possible.

chrome/browser/bookmarks/bookmark_storage.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_STORAGE_H_
 #define CHROME_BROWSER_BOOKMARKS_BOOKMARK_STORAGE_H_
 
 #include "base/files/important_file_writer.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "chrome/browser/bookmarks/bookmark_index.h"
 
+class BookmarkIndex;
 class BookmarkModel;
 class BookmarkPermanentNode;
 
 namespace base {
 class SequencedTaskRunner;
 }
 
 namespace content {
 class BrowserContext;
 }
@@ skipping 122 matching lines @@
   // See class description of BookmarkLoadDetails for details on this.
   scoped_ptr<BookmarkLoadDetails> details_;
 
   // Sequenced task runner where file I/O operations will be performed at.
   scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(BookmarkStorage);
 };
 
 #endif  // CHROME_BROWSER_BOOKMARKS_BOOKMARK_STORAGE_H_