Add module for counting date-last-roll-call and persisting those counts

components/update_client/persisted_data.h

Index: components/update_client/persisted_data.h
diff --git a/components/update_client/persisted_data.h b/components/update_client/persisted_data.h
new file mode 100644
index 0000000000000000000000000000000000000000..d4673b4f373a339cac41ae8c63d3440e20b5af0d
--- /dev/null
+++ b/components/update_client/persisted_data.h
@@ -0,0 +1,60 @@
+// Copyright 2016 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_UPDATE_CLIENT_PERSISTED_DATA_H_
+#define COMPONENTS_UPDATE_CLIENT_PERSISTED_DATA_H_
+
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
+#include "base/values.h"
+
+class PrefRegistrySimple;
+class PrefService;
+
+namespace update_client {
+
+// A PersistedData is a wrapper layer around a PrefService, designed to maintain
+// update data that outlives the browser process and isn't exposed outside of
+// update_client.
+//
+// The public methods of this class should be called only on the thread that
+// initializes it - which also has to match the thread the PrefService has been
+// initialized on.
+class PersistedData {
+ public:
+  // Constructs a provider that uses the specified |pref_service|.
+  // The associated preferences are assumed to already be registered.
+  // The |pref_service| must outlive the entire update_client.
+  explicit PersistedData(PrefService* pref_service);
+
+  ~PersistedData();
+
+  // Returns the DateLastRollCall (the server-localized calendar date number the
+  // |id| was last checked by this client on) for the specified |id|.
+  // -2 indicates that there is no recorded date number for the |id|.
+  int GetDateLastRollCall(const std::string& id) const;
+
+  // Records the DateLastRollCall for the specified |ids|. |datenum| must be a
+  // non-negative integer: calls with a negative |datenum| are simply ignored.
+  // Calls to SetDateLastRollCall that occur prior to the persisted data store
+  // has been fully initialized are ignored.
+  void SetDateLastRollCall(const std::vector<std::string>& ids,
+                           int datenum) const;
+
+  // This is called only via update_client's RegisterUpdateClientPreferences.
+  static void RegisterPrefs(PrefRegistrySimple* registry);
+
+ private:
+  base::ThreadChecker thread_checker_;
+  PrefService* pref_service_;
+
+  DISALLOW_COPY_AND_ASSIGN(PersistedData);
+};
+
+}  // namespace update_client
+
+#endif  // COMPONENTS_UPDATE_CLIENT_PERSISTED_DATA_H_