sync: Introduce classes for per-type counters

sync/internal_api/public/sessions/status_counters.h

+// Copyright 2014 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 SYNC_INTERNAL_API_PUBLIC_SESSIONS_STATUS_COUNTERS_H_
+#define SYNC_INTERNAL_API_PUBLIC_SESSIONS_STATUS_COUNTERS_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/values.h"
+#include "sync/base/sync_export.h"
+
+namespace syncer {
+
+// A class to maintain counts related to the current status of a sync type.
+struct SYNC_EXPORT_PRIVATE StatusCounters {
+  StatusCounters();
+  ~StatusCounters();
+
+  scoped_ptr<base::DictionaryValue> ToValue() const;
+  std::string ToString() const;
+
+  size_t num_total_entries;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_SESSIONS_STATUS_COUNTERS_H_