Record the tab state during data use

components/data_use_measurement/core/data_use_measurement.cc

Index: components/data_use_measurement/core/data_use_measurement.cc
diff --git a/components/data_use_measurement/core/data_use_measurement.cc b/components/data_use_measurement/core/data_use_measurement.cc
index c7f1f69579d3d9dd0bb00fac9253247e6867cf74..92270a60016add6736e5f99a5e50cc61ac0cc0f8 100644
--- a/components/data_use_measurement/core/data_use_measurement.cc
+++ b/components/data_use_measurement/core/data_use_measurement.cc
@@ -8,6 +8,8 @@
 #include "base/metrics/sparse_histogram.h"
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
+#include "components/data_use_measurement/core/data_use_ascriber.h"
+#include "components/data_use_measurement/core/data_use_recorder.h"
 #include "components/data_use_measurement/core/data_use_user_data.h"
 #include "components/data_use_measurement/core/url_request_classifier.h"
 #include "components/domain_reliability/uploader.h"
@@ -65,10 +67,12 @@ void IncrementLatencyHistogramByCount(const std::string& name,
 }  // namespace
 
 DataUseMeasurement::DataUseMeasurement(
+    DataUseAscriber* ascriber,

[RyanSturm, 2016/12/16 16:26:10]

nit: can you order the arguments in the same order as the initialization list;
i.e., move ascriber to be the last argument.

[Raj, 2016/12/16 19:59:10]

Done.

     std::unique_ptr<URLRequestClassifier> url_request_classifier,
     const metrics::UpdateUsagePrefCallbackType& metrics_data_use_forwarder)
     : url_request_classifier_(std::move(url_request_classifier)),
-      metrics_data_use_forwarder_(metrics_data_use_forwarder)
+      metrics_data_use_forwarder_(metrics_data_use_forwarder),
+      ascriber_(ascriber)
 #if defined(OS_ANDROID)
       ,
       app_state_(base::android::APPLICATION_STATE_HAS_RUNNING_ACTIVITIES),
@@ -81,6 +85,7 @@ DataUseMeasurement::DataUseMeasurement(
       no_reads_since_background_(false)
 #endif
 {
+  DCHECK(ascriber_);
   DCHECK(url_request_classifier_);
 }
 
@@ -190,6 +195,16 @@ void DataUseMeasurement::ReportDataUseUMA(const net::URLRequest& request,
     }
   }
 #endif
+
+  if (is_user_traffic) {
+    const auto recorder = ascriber_->GetDataUseRecorderIfExists(&request);

[RyanSturm, 2016/12/16 16:26:10]

nit: s/auto/DataUseRecorder*/

It's a little fuzzy in the style guide whether the method name Get<type>IfExists
is enough to allow auto:
https://google.github.io/styleguide/cppguide.html#auto

[Raj, 2016/12/16 19:59:10]

Done.

+    if (recorder) {
+      RecordTabStateHistogram(
+          dir, new_app_state,
+          recorder->is_visible() ? TabState::FOREGROUND : TabState::BACKGROUND,
+          bytes);
+    }
+  }
 }
 
 void DataUseMeasurement::UpdateDataUsePrefs(
@@ -330,4 +345,23 @@ void DataUseMeasurement::ReportDataUsageServices(
   }
 }
 
+void DataUseMeasurement::RecordTabStateHistogram(
+    TrafficDirection dir,
+    DataUseUserData::AppState app_state,
+    TabState tab_state,
+    int64_t bytes) {
+  if (app_state == DataUseUserData::UNKNOWN || tab_state == TabState::UNKNOWN)
+    return;
+
+  RecordUMAHistogramCount(
+      base::StringPrintf("DataUse.AppTabState.%s.%s",

[RyanSturm, 2016/12/16 16:26:10]

This expression might be a little more readable if you built the histogram
string in steps.

std::string histogram_name = "DataUse.AppTabState.";
histogram_name.append(...)
if (app_state == brackground)
{...}
else
{...}

RecordUMAHistogramCount(histogram_name...)

[Raj, 2016/12/16 19:59:10]

Done.

[RyanSturm, 2016/12/19 19:31:49]

Thanks.

+                         dir == UPSTREAM ? "Upstream" : "Downstream",
+                         app_state == DataUseUserData::BACKGROUND
+                             ? "AppBackground"
+                             : tab_state == TabState::FOREGROUND
+                                   ? "AppForeground.TabForeground"
+                                   : "AppForeground.TabBackground"),
+      bytes);
+}
+
 }  // namespace data_use_measurement