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.h"

[sdefresne, 2016/09/19 17:07:52]

I think you can include base/callback_forward.h here and include base/callback.h
in the implementation file instead (may have to include in multiple
implementation files).

[ioanap, 2016/09/20 09:36:48]

Done.

+#include "components/browsing_data/core/counters/browsing_data_counter.h"

[sdefresne, 2016/09/19 17:07:52]

You don't call any method of BrowsingDataCounter in that file, so you can
probably forward-declare it and move the include in the implementation file
(files?).

[ioanap, 2016/09/20 09:36:48]

I don't call any method, but I need a nested class from it:
BrowsingDataCounter::Result.

+
+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:
+  typedef base::Callback<void(

[sdefresne, 2016/09/19 17:07:52]

nit: I think using is recommended instead of typedef now (easier to read)

  using UpdateUICallback = base::Callback<void(const
browsing_data::BrowsingDataCounter::Result&)>;

[ioanap, 2016/09/20 09:36:48]

Didn't know that. Thank you!

+      const browsing_data::BrowsingDataCounter::Result&)>
+      UpdateUICallback;
+
+  // This method returns a nullptr if there is no corresponding counter for the
+  // data type specified by the |pref_name|.
+  static BrowsingDataCounterWrapper* CreateCounterWrapper(

[sdefresne, 2016/09/19 17:07:52]

Why is this method not returning a std::unique_ptr<>?

[ioanap, 2016/09/20 09:36:48]

Done.

+      const char* pref_name,
+      ios::ChromeBrowserState* browser_state,
+      PrefService* pref_service,
+      const UpdateUICallback update_ui_callback);

[sdefresne, 2016/09/19 17:07:52]

const UpdateUICallback& update_ui_callback

[ioanap, 2016/09/20 09:36:48]

Done.

+
+  ~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_;
+};

[sdefresne, 2016/09/19 17:07:52]

DISALLOW_COPY_AND_ASSIGN()?

[ioanap, 2016/09/20 09:36:48]

Done.

+
+#endif  // IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_COUNTER_WRAPPER_