Add UMA histograms for data usage tab model

chrome/browser/android/data_usage/data_use_tab_model.cc

Index: chrome/browser/android/data_usage/data_use_tab_model.cc
diff --git a/chrome/browser/android/data_usage/data_use_tab_model.cc b/chrome/browser/android/data_usage/data_use_tab_model.cc
index c4d8e36e39e2716ec47af99ce4fe3453efac5227..d41046807747e2442a5e599eb592e9cadbbdb451 100644
--- a/chrome/browser/android/data_usage/data_use_tab_model.cc
+++ b/chrome/browser/android/data_usage/data_use_tab_model.cc
@@ -4,7 +4,7 @@
 
 #include "chrome/browser/android/data_usage/data_use_tab_model.h"
 
-#include "base/time/time.h"
+#include "base/metrics/histogram_macros.h"
 #include "chrome/browser/android/data_usage/external_data_use_observer.h"
 #include "chrome/browser/android/data_usage/tab_data_use_entry.h"
 
@@ -19,16 +19,19 @@ bool IsValidTabID(int32_t tab_id) {
   return tab_id >= 0;
 }
 
+const char kUMAExpiredInactiveTabEntryRemovalDurationSecondsHistogram[] =
+    "DataUse.TabModel.ExpiredInactiveTabEntryRemovalDuration";
+const char kUMAExpiredActiveTabEntryRemovalDurationHoursHistogram[] =
+    "DataUse.TabModel.ExpiredActiveTabEntryRemovalDuration";
+const char kUMAUnexpiredTabEntryRemovalDurationMinutesHistogram[] =
+    "DataUse.TabModel.UnexpiredTabEntryRemovalDuration";
+
 }  // namespace
 
 namespace chrome {
 
 namespace android {
 
-size_t DataUseTabModel::GetMaxTabEntriesForTests() {
-  return kMaxTabEntries;
-}
-
 DataUseTabModel::DataUseTabModel(
     const ExternalDataUseObserver* data_use_observer,
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner)
@@ -125,6 +128,14 @@ void DataUseTabModel::RemoveObserver(TabDataUseObserver* observer) {
   observer_list_->RemoveObserver(observer);
 }
 
+base::TimeTicks DataUseTabModel::Now() const {
+  return base::TimeTicks::Now();
+}
+
+size_t DataUseTabModel::GetMaxTabEntriesForTests() {
+  return kMaxTabEntries;
+}
+
 void DataUseTabModel::NotifyObserversOfTrackingStarting(int32_t tab_id) {
   observer_list_->Notify(FROM_HERE, &TabDataUseObserver::NotifyTrackingStarting,
                          tab_id);
@@ -168,10 +179,26 @@ 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() <= kMaxTabEntries)
@@ -189,6 +216,10 @@ void DataUseTabModel::CompactTabEntries() {
       }
     }
     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);
   }
 }