Amortize data usage using TrafficStats on Android.

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index cd92dbbecc9983922294f4b0ba6bec6c886be996..e7814e2428147dabb40a564e39e619fea61ed306 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -43,6 +43,7 @@
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_prefs.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_params.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.h"
+#include "components/data_usage/core/data_use_amortizer.h"
 #include "components/net_log/chrome_net_log.h"
 #include "components/policy/core/common/policy_service.h"
 #include "components/proxy_config/pref_proxy_config_tracker.h"
@@ -115,6 +116,7 @@
 #include "base/android/build_info.h"
 #include "chrome/browser/android/datausage/external_data_use_observer.h"
 #include "chrome/browser/android/net/external_estimate_provider_android.h"
+#include "components/data_usage/android/traffic_stats_amortizer.h"
 #endif
 
 #if defined(OS_CHROMEOS)
@@ -606,9 +608,15 @@ void IOThread::Init() {
       extension_event_router_forwarder_;
 #endif
 
+  scoped_ptr<data_usage::DataUseAmortizer> data_use_amortizer;
+#if defined(OS_ANDROID)
+  data_use_amortizer.reset(new data_usage::android::TrafficStatsAmortizer());

[bengr, 2015/11/10 18:12:50]

It would be better if you didn't specialize for Android here, and instead passed
this in via the IOThread constructor or Globals. Likewise for the
external_data_use_observer_.

[tbansal1, 2015/11/10 18:53:55]

Why can this not be constructed in DataUseAggregator constructor (instead of
IOthread constructing it and passing it)?

[sclittle, 2015/11/11 02:10:07]

I don't think I understand what you mean. It has to be specialized for Android
somewhere, and if it's specialized here, then no where else has to hold on to a
scoped_ptr<DataUseAmortizer>.

Plus, the aggregator takes ownership of the amortizer, so it would be an empty
scoped_ptr<DataUseAmortizer> in Globals/IOThread most of the time.

[sclittle, 2015/11/11 02:10:07]

Because the DataUseAggregator doesn't have visibility into the
components/data_usage/android directory, since that would be a cyclical
dependency.

[bengr, 2015/11/11 15:41:37]

I was hoping that you could set up the platform specialization in
ChromeBrowserMainParts::PreCreateThreadsImpl() or somewhere nearby, but it
doesn't look like there's an established pattern.

+#endif
+
   data_use_aggregator_.reset(new data_usage::DataUseAggregator(
       scoped_ptr<data_usage::DataUseAnnotator>(
-          new chrome_browser_data_usage::TabIdAnnotator())));
+          new chrome_browser_data_usage::TabIdAnnotator()),
+      data_use_amortizer.Pass()));
 
   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466432
   // is fixed.