Add UMA histograms for data usage tab model

chrome/browser/android/data_usage/tab_data_use_entry.cc

 // 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.
 
 #include "chrome/browser/android/data_usage/tab_data_use_entry.h"
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "chrome/browser/android/data_usage/external_data_use_observer.h"
 #include "components/variations/variations_associated_data.h"
 
 namespace {
 
 // Indicates the default maximum number of tracking session history to maintain
 // per tab. May be overridden by the field trial.
 const size_t kDefaultMaxSessionsPerTab = 5;
 
 // Indicates the default expiration duration in seconds, after which it can be
 // sweeped from history for a closed tab entry and an open tab entry
 // respectively. May be overridden by the field trial.
 const unsigned int kDefaultClosedTabExpirationDurationSeconds =
     30;  // 30 seconds.
 const unsigned int kDefaultOpenTabExpirationDurationSeconds =
     60 * 60 * 24 * 5;  // 5 days.
 
+const char kUMATrackingSessionLifetimeSecondsHistogram[] =
+    "DataUse.TabModel.TrackingSessionLifetime";
+const char kUMAOldInactiveSessionRemovalDurationSecondsHistogram[] =
+    "DataUse.TabModel.OldInactiveSessionRemovalDuration";
+
 // Returns various parameters from the values specified in the field trial.
 size_t GetMaxSessionsPerTab() {
   size_t max_sessions_per_tab = -1;
   std::string variation_value = variations::GetVariationParamValue(
       chrome::android::ExternalDataUseObserver::
           kExternalDataUseObserverFieldTrial,
       "max_sessions_per_tab");
   if (!variation_value.empty() &&
       base::StringToSizeT(variation_value, &max_sessions_per_tab)) {
     return max_sessions_per_tab;
@@ skipping 66 matching lines @@
 bool TabDataUseEntry::EndTracking() {
   DCHECK(tab_close_time_.is_null());
   if (!IsTrackingDataUse())
     return false;  // Duplicate end events.
 
   TabSessions::reverse_iterator back_iterator = sessions_.rbegin();
   if (back_iterator == sessions_.rend())
     return false;
 
   back_iterator->end_time = Now();
+
+  UMA_HISTOGRAM_CUSTOM_TIMES(
+      kUMATrackingSessionLifetimeSecondsHistogram,
+      back_iterator->end_time - back_iterator->start_time,
+      base::TimeDelta::FromSeconds(1), base::TimeDelta::FromHours(1), 50);
+
   return true;
 }
 
 bool TabDataUseEntry::EndTrackingWithLabel(const std::string& label) {
   if (!sessions_.empty() && sessions_.back().label == label)
     return EndTracking();
   return false;
 }
 
 void TabDataUseEntry::OnTabCloseEvent() {
   DCHECK(!IsTrackingDataUse());
   tab_close_time_ = Now();
 }
 
 bool TabDataUseEntry::IsExpired() const {
   const base::TimeTicks now = Now();
 
   if (!tab_close_time_.is_null()) {
     // Closed tab entry.
     return ((now - tab_close_time_) > closed_tab_expiration_duration_);
   }
 
   const base::TimeTicks latest_session_time = GetLatestStartOrEndTime();
   if (latest_session_time.is_null() ||
       ((now - latest_session_time) > open_tab_expiration_duration_)) {
-    // TODO(rajendrant): Add UMA to track deletion of entries corresponding to
-    // existing tabs.
     return true;
   }
   return false;
 }
 
 bool TabDataUseEntry::GetLabel(const base::TimeTicks& data_use_time,
                                std::string* output_label) const {
   *output_label = "";
 
   // Find a tracking session in history that was active at |data_use_time|.
@@ skipping 28 matching lines @@
   if (back_iterator == sessions_.rend())
     return base::TimeTicks();  // No tab session found.
   if (!back_iterator->end_time.is_null())
     return back_iterator->end_time;
 
   DCHECK(!back_iterator->start_time.is_null());
   return back_iterator->start_time;
 }
 
 void TabDataUseEntry::CompactSessionHistory() {
-  // TODO(rajendrant): Add UMA to track how often old sessions are lost.
-  while (sessions_.size() > max_sessions_per_tab_)
+  while (sessions_.size() > max_sessions_per_tab_) {
+    const auto& front = sessions_.front();
+    DCHECK(!front.end_time.is_null());
+    // Track how often old sessions are lost.
+    UMA_HISTOGRAM_CUSTOM_TIMES(
+        kUMAOldInactiveSessionRemovalDurationSecondsHistogram,
+        Now() - front.end_time, base::TimeDelta::FromSeconds(1),
+        base::TimeDelta::FromHours(1), 50);
     sessions_.pop_front();
+  }
 }
 
 }  // namespace android
 
 }  // namespace chrome