Add external data use observer

components/data_usage/core/data_use_aggregator.h

 // 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>
@@ skipping 32 matching lines @@
                              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);
 
+  // Passes the ownership of an external observer to DataUseAggregator.
+  void PassExternalObserver(scoped_ptr<Observer> external_observer);
+
  private:
   void NotifyDataUse(const std::vector<DataUse>& data_use_sequence);
 
   base::ThreadChecker thread_checker_;
   base::ObserverList<Observer> observer_list_;
 
+  // An observer which is external to Chromium.
+  scoped_ptr<Observer> external_observer_;

[sclittle, 2015/10/09 22:59:28]

Making the DataUseAggregator own one of its observers actually gets quite weird,
especially around destruction time. The Observer's destructor (which calls
data_use_aggregator_->RemoveObserver) will run after the DataUseAggregator's
destructor, which will probably explode.

[tbansal1, 2015/10/12 16:47:36]

changed the owner to IO thread globals.

+
   DISALLOW_COPY_AND_ASSIGN(DataUseAggregator);
 };
 
 }  // namespace data_usage
 
 #endif  // COMPONENTS_DATA_USAGE_CORE_DATA_USE_AGGREGATOR_H_