[Offline pages] Fixing a crash in URL change, when offline copy not present

components/offline_pages/offline_page_model.cc

 // Copyright 2015 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/offline_pages/offline_page_model.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 459 matching lines @@
     return;
   }
   MarkPageForDeletion(node->id(), base::Bind(&EmptyDeleteCallback));
 }
 
 void OfflinePageModel::BookmarkNodeChanged(
     bookmarks::BookmarkModel* model,
     const bookmarks::BookmarkNode* node) {
   // BookmarkNodeChanged could be triggered if title or URL gets changed. If
   // the latter, we need to invalidate the offline copy.
-  DCHECK(offline_pages_.count(node->id()) > 0);
-  if (offline_pages_[node->id()].url != node->url())
+  auto iter = offline_pages_.find(node->id());
+  if (iter != offline_pages_.end() && iter->second.url != node->url())
     DeletePageByBookmarkId(node->id(), DeletePageCallback());
 }
 
 void OfflinePageModel::OnEnsureArchivesDirCreatedDone() {
   store_->Load(base::Bind(&OfflinePageModel::OnLoadDone,
                           weak_ptr_factory_.GetWeakPtr()));
 }
 
 void OfflinePageModel::OnLoadDone(
     OfflinePageMetadataStore::LoadStatus load_status,
@@ skipping 182 matching lines @@
 }
 
 void OfflinePageModel::CacheLoadedData(
     const std::vector<OfflinePageItem>& offline_pages) {
   offline_pages_.clear();
   for (const auto& offline_page : offline_pages)
     offline_pages_[offline_page.bookmark_id] = offline_page;
 }
 
 }  // namespace offline_pages