Add "Show saved copy" button in dino page when there's offline copy

components/offline_pages/offline_page_model.h

 // 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.
 
 #ifndef COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_H_
 #define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 155 matching lines @@
                               const DeletePageCallback& callback);
 
   // Deletes offline pages related to the passed |bookmark_ids|. Requires that
   // the model is loaded.
   void DeletePagesByBookmarkId(const std::vector<int64>& bookmark_ids,
                                const DeletePageCallback& callback);
 
   // Wipes out all the data by deleting all saved files and clearing the store.
   void ClearAll(const base::Closure& callback);
 
+  // Returns true if there're offline pages.
+  bool HasOfflinePages() const;
+
   // Gets all available offline pages. Requires that the model is loaded.
   const std::vector<OfflinePageItem> GetAllPages() const;
 
   // Gets pages that should be removed to clean up storage. Requires that the
   // model is loaded.
   const std::vector<OfflinePageItem> GetPagesToCleanUp() const;
 
   // Returns an offline page associated with a specified |bookmark_id|. nullptr
   // is returned if not found.
   const OfflinePageItem* GetPageByBookmarkId(int64 bookmark_id) const;
 
   // Returns an offline page that is stored as |offline_url|. A nullptr is
   // returned if not found.
   const OfflinePageItem* GetPageByOfflineURL(const GURL& offline_url) const;
 
+  // Returns an offline page saved for |online_url|. A nullptr is returned if
+  // not found.
+  const OfflinePageItem* GetPageByOnlineURL(const GURL& online_url) const;
+
   // Checks that all of the offline pages have corresponding offline copies.
   // If a page is discovered to be missing an offline copy, its offline page
   // metadata will be removed and |OfflinePageDeleted| will be sent to model
   // observers.
   void CheckForExternalFileDeletion();
 
   // Methods for testing only:
   OfflinePageMetadataStore* GetStoreForTesting();
 
   bool is_loaded() const { return is_loaded_; }
@@ skipping 107 matching lines @@
       scoped_observer_;
 
   base::WeakPtrFactory<OfflinePageModel> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OfflinePageModel);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_H_