[Offline] Creates metadata store interface for offline pages

components/offline_pages/offline_page_metadata_store.h

Index: components/offline_pages/offline_page_metadata_store.h
diff --git a/components/offline_pages/offline_page_metadata_store.h b/components/offline_pages/offline_page_metadata_store.h
new file mode 100644
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+// 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_METADATA_STORE_H_
+#define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_METADATA_STORE_H_
+
+#include <vector>
+
+#include "base/callback.h"
+
+class GURL;
+
+namespace offline_pages {
+
+struct OfflinePageItem;
+
+// OfflinePageMetadataStore keeps metadata for the offline pages.
+// Ability to create multiple instances of the store as well as behavior of
+// asynchronous operations when the object is being destroyed, before such
+// operation finishes will depend on implementation. It should be possbile to
+// issue multiple asynchronous operations in parallel.
+class OfflinePageMetadataStore {
+ public:
+  typedef base::Callback<void(bool, const std::vector<OfflinePageItem>&)>
+      LoadCallback;
+  typedef base::Callback<void(bool)> UpdateCallback;
+
+  OfflinePageMetadataStore();
+  virtual ~OfflinePageMetadataStore();
+
+  // Get all of the offline pages from the store.
+  virtual void Load(const LoadCallback& callback) = 0;
+
+  // Asynchronously adds offline page metadata to the store for a given URL.
+  // Result of the update is passed in callback.
+  virtual void AddOfflinePage(const OfflinePageItem& offline_page,
+                              const UpdateCallback& callback) = 0;
+
+  // Asynchronously removes offline page metadata from the store.
+  // Result of the update is passed in callback.
+  virtual void RemoveOfflinePage(const GURL& page_url,
+                                 const UpdateCallback& callback) = 0;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_METADATA_STORE_H_