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"
 
 namespace {
 
 // Indicates the maximum number of tracking session history to maintain per tab.
 const size_t kMaxSessionsPerTab = 5;
 
 // Indicates the expiration duration in seconds for a closed tab entry, after
 // which it can be sweeped from history.
 const unsigned int kClosedTabExpirationDurationSeconds = 30;  // 30 seconds.
 
 // Indicates the expiration duration in seconds for an open tab entry, after
 // which it can be sweeped from history.
 const unsigned int kOpenTabExpirationDurationSeconds =
     60 * 60 * 24 * 5;  // 5 days.
 
+const char kUMATrackingSessionLifetimeSecondsHistogram[] =

[tbansal1, 2015/11/16 17:17:38]

Remove Seconds/Minutes etc. from the variable names.

[Raj, 2015/11/16 20:09:37]

Not sure. Each UMA needs different precision.

+    "DataUse.TabModel.TrackingSessionLifetime";
+const char kUMAOldInactiveSessionRemovaltimeSecondsHistogram[] =
+    "DataUse.TabModel.OldInactiveSessionRemovaltime";
+
 }  // namespace
 
 namespace chrome {
 
 namespace android {
 
 size_t TabDataUseEntry::GetMaxSessionsPerTabForTests() {
   return kMaxSessionsPerTab;
 }
 
@@ skipping 34 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_COUNTS_1000(

[tbansal1, 2015/11/16 17:17:38]

TIMES?

[Raj, 2015/11/16 20:09:36]

Tracking session lifetime in the range of 1 second to 16.67 minutes.

+      kUMATrackingSessionLifetimeSecondsHistogram,
+      base::TimeDelta(back_iterator->end_time - back_iterator->start_time)
+          .InSeconds());
+
   return true;
 }
 
 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_) >
             base::TimeDelta::FromSeconds(kClosedTabExpirationDurationSeconds));
   }
 
   const base::TimeTicks latest_session_time = GetLatestStartOrEndTime();
   if (latest_session_time.is_null() ||
       ((now - latest_session_time) >
        base::TimeDelta::FromSeconds(kOpenTabExpirationDurationSeconds))) {
-    // 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() > kMaxSessionsPerTab)
+  while (sessions_.size() > kMaxSessionsPerTab) {
+    const auto& front = sessions_.front();
+    DCHECK(!front.end_time.is_null());
+    // Track how often old sessions are lost.
+    UMA_HISTOGRAM_COUNTS_1000(
+        kUMAOldInactiveSessionRemovaltimeSecondsHistogram,

[tbansal1, 2015/11/16 17:17:38]

TIMES?

[Raj, 2015/11/16 20:09:36]

Tracking old inactive tracking session removal times in the range 1 second to
16.67
minutes.

+        base::TimeDelta(Now() - front.end_time).InSeconds());
     sessions_.pop_front();
+  }
 }
 
 }  // namespace android
 
 }  // namespace chrome