[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
index 0000000000000000000000000000000000000000..93d01ab1ed2c420fadd6bb5571dfcc46dddfce14
--- /dev/null
+++ b/components/offline_pages/offline_page_metadata_store.h
@@ -0,0 +1,44 @@
+// 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.

[Dmitry Titov, 2015/06/08 21:47:21]

Would be nice to add details, for example:
- is it used as singleton or multiple independent ones will be created?
- Lifetime - for example, will the AddOfflinePage be successful if the caller
destroys an instance of this class w/o waiting for UpdateCallback?

[fgorski, 2015/06/09 20:12:17]

Done.

I added a comment that nothing like that is expected at the interface level, but
that calling operations in parallel should be possible.

+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.

[Dmitry Titov, 2015/06/08 21:47:21]

Since these methods are async, it's useful to document the allowed usage
patterns:
- can those be issued in parallel
- what is expected result of load/update/load sequence that does not wait for
callbacks in between?

[fgorski, 2015/06/09 20:12:18]

Done.

+  virtual void Load(const LoadCallback& callback) = 0;
+
+  // 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;
+
+  // 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_