Create component to expose network usage stats to consumers.

components/data_usage/core/data_use_aggregator.h

Index: components/data_usage/core/data_use_aggregator.h
diff --git a/components/data_usage/core/data_use_aggregator.h b/components/data_usage/core/data_use_aggregator.h
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+// 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_DATA_USAGE_CORE_DATA_USE_AGGREGATOR_H_
+#define COMPONENTS_DATA_USAGE_CORE_DATA_USE_AGGREGATOR_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "base/threading/thread_checker.h"
+#include "components/data_usage/core/data_use.h"
+
+namespace net {
+class URLRequest;
+}
+
+namespace data_usage {
+
+// Class that collects and aggregates network usage, reporting the usage to
+// observers. Should only be used on the IO thread.
+class DataUseAggregator {
+ public:
+  class Observer {
+   public:
+    virtual ~Observer() {}
+    // TODO(sclittle): Consider performing some pre-aggregation on the data use.
+    virtual void OnDataUse(const std::vector<DataUse>& data_use_sequence) = 0;
+  };
+
+  DataUseAggregator();
+  virtual ~DataUseAggregator();
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+  // Virtual for testing.
+  virtual void ReportDataUse(const net::URLRequest& request,
+                             int32_t tab_id,
+                             int64_t tx_bytes,
+                             int64_t rx_bytes);
+
+  // Account for off-the-record data use. This usage is only kept track of here
+  // so that it can be taken out of any amortized data usage calculations, and a
+  // per-request breakdown of off-the-record data usage will never leave the
+  // DataUseAggregator.
+  // Virtual for testing.
+  virtual void ReportOffTheRecordDataUse(int64_t tx_bytes, int64_t rx_bytes);
+
+ private:
+  void NotifyDataUse(const std::vector<DataUse>& data_use_sequence);
+
+  base::ThreadChecker thread_checker_;
+  base::ObserverList<Observer> observer_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(DataUseAggregator);
+};
+
+}  // namespace data_usage
+
+#endif  // COMPONENTS_DATA_USAGE_CORE_DATA_USE_AGGREGATOR_H_