Change ImageStore to use SequenceChecker instead of ThreadChecker.

components/enhanced_bookmarks/image_store.cc

 // Copyright 2014 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 "components/enhanced_bookmarks/image_store.h"
 
 #include "url/gurl.h"
 
 ImageStore::ImageStore() {
 }
 
 ImageStore::~ImageStore() {
 }
 
 void ImageStore::ChangeImageURL(const GURL& from, const GURL& to) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 
   if (!HasKey(from))
     return;
 
   std::pair<gfx::Image, GURL> image_info = Get(from);
   Erase(from);
   Insert(to, image_info.second, image_info.first);
 }