Add a browsing data counter factory on iOS

ios/chrome/browser/browsing_data/browsing_data_counter_wrapper.h

+// 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 IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_COUNTER_WRAPPER_H_
+#define IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_COUNTER_WRAPPER_H_
+
+#include <memory>
+#include <string>
+
+#include "base/callback_forward.h"
+#include "components/browsing_data/core/counters/browsing_data_counter.h"
+
+class PrefService;
+
+namespace ios {
+class ChromeBrowserState;
+}
+
+// Wrapper around a browsing data volume counter that bridges the update counter
+// UI callback to the UI.
+class BrowsingDataCounterWrapper {
+ public:
+  using UpdateUICallback =
+      base::Callback<void(const browsing_data::BrowsingDataCounter::Result&)>;
+
+  // This method returns a nullptr if there is no corresponding counter for the

[sdefresne, 2016/09/20 11:50:46]

nit: We usually do not use "nullptr" in comments, so I would just write
something like

// This method returns the counter corresponding to the data type specified by
// |pref_name| or null if there is no such counter.

[ioanap, 2016/09/20 12:43:29]

Done.

+  // data type specified by the |pref_name|.
+  static std::unique_ptr<BrowsingDataCounterWrapper> CreateCounterWrapper(
+      const char* pref_name,
+      ios::ChromeBrowserState* browser_state,
+      PrefService* pref_service,
+      const UpdateUICallback& update_ui_callback);
+
+  ~BrowsingDataCounterWrapper();
+
+  void RestartCounter();
+
+ private:
+  BrowsingDataCounterWrapper(
+      std::unique_ptr<browsing_data::BrowsingDataCounter> counter,
+      PrefService* pref_service,
+      const UpdateUICallback& update_ui_callback);
+
+  // Method to be passed as callback to the counter. This will be invoked when
+  // the result is ready.
+  void UpdateWithResult(
+      std::unique_ptr<browsing_data::BrowsingDataCounter::Result> result);
+
+  // The counter for which the interaction is managed by this wrapper.
+  std::unique_ptr<browsing_data::BrowsingDataCounter> counter_;
+
+  // Callback that updates the UI once the counter result is ready. This is
+  // invoked by UpdateWithResult.
+  UpdateUICallback update_ui_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(BrowsingDataCounterWrapper);
+};
+
+#endif  // IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_COUNTER_WRAPPER_