Add UMA histograms for data usage tab model

chrome/browser/android/data_usage/data_use_tab_model.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/data_use_tab_model.h"
 
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/time/time.h"
 #include "chrome/browser/android/data_usage/external_data_use_observer.h"
 #include "chrome/browser/android/data_usage/tab_data_use_entry.h"
 #include "components/variations/variations_associated_data.h"
 
 namespace {
 
 // Indicates the default maximum number of tabs to maintain session information
 // about. May be overridden by the field trial.
 const size_t kDefaultMaxTabEntries = 200;
 
+const char kUMAExpiredInactiveTabEntryRemovalDurationSecondsHistogram[] =
+    "DataUse.TabModel.ExpiredInactiveTabEntryRemovalDuration";
+const char kUMAExpiredActiveTabEntryRemovalDurationHoursHistogram[] =
+    "DataUse.TabModel.ExpiredActiveTabEntryRemovalDuration";
+const char kUMAUnexpiredTabEntryRemovalDurationMinutesHistogram[] =
+    "DataUse.TabModel.UnexpiredTabEntryRemovalDuration";
+
 // Returns true if |tab_id| is a valid tab ID.
 bool IsValidTabID(int32_t tab_id) {
   return tab_id >= 0;
 }
 
 // Returns various parameters from the values specified in the field trial.
 size_t GetMaxTabEntries() {
   size_t max_tab_entries = -1;
   std::string variation_value = variations::GetVariationParamValue(
       chrome::android::ExternalDataUseObserver::
@@ skipping 115 matching lines @@
 }
 
 void DataUseTabModel::AddObserver(TabDataUseObserver* observer) {
   observer_list_->AddObserver(observer);
 }
 
 void DataUseTabModel::RemoveObserver(TabDataUseObserver* observer) {
   observer_list_->RemoveObserver(observer);
 }
 
+base::TimeTicks DataUseTabModel::Now() const {
+  return base::TimeTicks::Now();
+}
+
 void DataUseTabModel::NotifyObserversOfTrackingStarting(int32_t tab_id) {
   observer_list_->Notify(FROM_HERE, &TabDataUseObserver::NotifyTrackingStarting,
                          tab_id);
 }
 
 void DataUseTabModel::NotifyObserversOfTrackingEnding(int32_t tab_id) {
   observer_list_->Notify(FROM_HERE, &TabDataUseObserver::NotifyTrackingEnding,
                          tab_id);
 }
 
@@ skipping 23 matching lines @@
   if (tab_entry_iterator != active_tabs_.end() &&
       tab_entry_iterator->second.EndTracking()) {
     NotifyObserversOfTrackingEnding(tab_id);
   }
 }
 
 void DataUseTabModel::CompactTabEntries() {
   // Remove expired tab entries.
   for (TabEntryMap::iterator tab_entry_iterator = active_tabs_.begin();
        tab_entry_iterator != active_tabs_.end();) {
-    if (tab_entry_iterator->second.IsExpired())
+    const auto& tab_entry = tab_entry_iterator->second;
+    if (tab_entry.IsExpired()) {
+      // Track the lifetime of expired tab entry.
+      const base::TimeDelta removal_time =
+          Now() - tab_entry.GetLatestStartOrEndTime();
+      if (!tab_entry.IsTrackingDataUse()) {
+        UMA_HISTOGRAM_CUSTOM_TIMES(
+            kUMAExpiredInactiveTabEntryRemovalDurationSecondsHistogram,
+            removal_time, base::TimeDelta::FromSeconds(1),
+            base::TimeDelta::FromHours(1), 50);
+      } else {
+        UMA_HISTOGRAM_CUSTOM_TIMES(
+            kUMAExpiredActiveTabEntryRemovalDurationHoursHistogram,
+            removal_time, base::TimeDelta::FromHours(1),
+            base::TimeDelta::FromDays(5), 50);
+      }
       active_tabs_.erase(tab_entry_iterator++);
-    else
+    } else {
       ++tab_entry_iterator;
+    }
   }
 
   if (active_tabs_.size() <= max_tab_entries_)
     return;
 
   // Remove oldest unexpired tab entries.
   while (active_tabs_.size() > max_tab_entries_) {
     // Find oldest tab entry.
     TabEntryMap::iterator oldest_tab_entry_iterator = active_tabs_.begin();
     for (TabEntryMap::iterator tab_entry_iterator = active_tabs_.begin();
          tab_entry_iterator != active_tabs_.end(); ++tab_entry_iterator) {
       if (oldest_tab_entry_iterator->second.GetLatestStartOrEndTime() >
           tab_entry_iterator->second.GetLatestStartOrEndTime()) {
         oldest_tab_entry_iterator = tab_entry_iterator;
       }
     }
     DCHECK(oldest_tab_entry_iterator != active_tabs_.end());
+    UMA_HISTOGRAM_CUSTOM_TIMES(
+        kUMAUnexpiredTabEntryRemovalDurationMinutesHistogram,
+        Now() - oldest_tab_entry_iterator->second.GetLatestStartOrEndTime(),
+        base::TimeDelta::FromMinutes(1), base::TimeDelta::FromHours(1), 50);
     active_tabs_.erase(oldest_tab_entry_iterator);
   }
 }
 
 }  // namespace android
 
 }  // namespace chrome