Remove obsolete histograms Discarding.(Discards/Reloads)Per10Minutes*.

These histograms are not actively used. Most of the time, no tab is
discarded in a 10 minutes interval. To assess the impact of future
changes to the discarding logic, it would be more useful to report
the number of discards and reloads per day.

Bug: 1088709
Change-Id: Ia1b2573c154e0b01c9b6d6039a9b2c041db94b48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514467Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823887}

chrome/browser/metrics/tab_stats_data_store.cc

@@ -32,8 +32,6 @@ TabStatsDataStore::TabsStats::TabsStats()
       max_tab_per_window(0U),
       window_count(0U),
       window_count_max(0U) {
-  tab_discard_counts.fill(0U);
-  tab_reload_counts.fill(0U);
 }
 TabStatsDataStore::TabsStats::TabsStats(const TabsStats& other) = default;
 
@@ -168,20 +166,6 @@ void TabStatsDataStore::ResetIntervalData(
     AddTabToIntervalMap(iter.first, GetTabID(iter.first), true, interval_map);
 }
 
-void TabStatsDataStore::OnTabDiscardStateChange(
-    LifecycleUnitDiscardReason discard_reason,
-    bool is_discarding) {
-  if (is_discarding)
-    tab_stats_.tab_discard_counts[static_cast<size_t>(discard_reason)]++;
-  else
-    tab_stats_.tab_reload_counts[static_cast<size_t>(discard_reason)]++;
-}
-
-void TabStatsDataStore::ClearTabDiscardAndReloadCounts() {
-  tab_stats_.tab_discard_counts.fill(0U);
-  tab_stats_.tab_reload_counts.fill(0U);
-}
-
 base::Optional<TabStatsDataStore::TabID> TabStatsDataStore::GetTabIDForTesting(
     content::WebContents* web_contents) {
   if (!base::Contains(existing_tabs_, web_contents))

chrome/browser/metrics/tab_stats_data_store.h

@@ -53,16 +53,6 @@ class TabStatsDataStore {
 
     // The maximum total number of windows opened at the same time.
     size_t window_count_max;
-
-    // The number of tabs discarded, per discard reason.
-    std::array<size_t,
-               static_cast<size_t>(LifecycleUnitDiscardReason::kMaxValue) + 1>
-        tab_discard_counts;
-
-    // The number of tabs reloaded after a discard, per discard reason.
-    std::array<size_t,
-               static_cast<size_t>(LifecycleUnitDiscardReason::kMaxValue) + 1>
-        tab_reload_counts;
   };
 
   // Structure describing the state of a tab during an interval of time.
@@ -129,14 +119,6 @@ class TabStatsDataStore {
   // Reset |interval_map| with the list of current tabs.
   void ResetIntervalData(TabsStateDuringIntervalMap* interval_map);
 
-  // Updates counters when the discarded state of a tab changes.
-  void OnTabDiscardStateChange(LifecycleUnitDiscardReason discard_reason,
-                               bool is_discarding);
-
-  // Clears the discard and reload counters. Called after reporting the counter
-  // values.
-  void ClearTabDiscardAndReloadCounts();
-
   const TabsStats& tab_stats() const { return tab_stats_; }
 
   base::Optional<TabID> GetTabIDForTesting(content::WebContents* web_contents);

chrome/browser/metrics/tab_stats_tracker.cc

@@ -108,29 +108,6 @@ const char
     TabStatsTracker::UmaStatsReportingDelegate::kWindowCountHistogramName[] =
         "Tabs.WindowCount";
 
-// Tab discard and reload histogram names in the same order as in discard reason
-// enum.
-const char* kTabDiscardCountHistogramNames[] = {
-    "Discarding.DiscardsPer10Minutes.Extension",
-    "Discarding.DiscardsPer10Minutes.Urgent",
-};
-
-const char* kTabReloadCountHistogramNames[] = {
-    "Discarding.ReloadsPer10Minutes.Extension",
-    "Discarding.ReloadsPer10Minutes.Urgent",
-};
-
-static_assert(base::size(kTabDiscardCountHistogramNames) ==
-                  static_cast<size_t>(LifecycleUnitDiscardReason::kMaxValue) +
-                      1,
-              "There must be an entry in kTabDiscardCountHistogramNames for "
-              "each discard reason.");
-static_assert(base::size(kTabReloadCountHistogramNames) ==
-                  static_cast<size_t>(LifecycleUnitDiscardReason::kMaxValue) +
-                      1,
-              "There must be an entry in kTabReloadCountHistogramNames for "
-              "each discard reason.");
-
 const TabStatsDataStore::TabsStats& TabStatsTracker::tab_stats() const {
   return tab_stats_data_store_->tab_stats();
 }
@@ -193,21 +170,11 @@ TabStatsTracker::TabStatsTracker(PrefService* pref_service)
   heartbeat_timer_.Start(FROM_HERE, kTabsHeartbeatReportingInterval,
                          base::BindRepeating(&TabStatsTracker::OnHeartbeatEvent,
                                              base::Unretained(this)));
-
-  // Report discarding stats every 10 minutes.
-  tab_discard_reload_stats_timer_.Start(
-      FROM_HERE, base::TimeDelta::FromMinutes(10),
-      base::BindRepeating(&TabStatsTracker::OnTabDiscardCountReportInterval,
-                          base::Unretained(this)));
-
-  g_browser_process->GetTabManager()->AddObserver(this);
 }
 
 TabStatsTracker::~TabStatsTracker() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   BrowserList::GetInstance()->RemoveObserver(this);
-
-  base::PowerMonitor::RemoveObserver(this);
 }
 
 // static
@@ -358,19 +325,6 @@ void TabStatsTracker::OnResume() {
       tab_stats_data_store_->tab_stats().total_tab_count);
 }
 
-// resource_coordinator::TabLifecycleObserver:
-void TabStatsTracker::OnDiscardedStateChange(
-    content::WebContents* contents,
-    ::mojom::LifecycleUnitDiscardReason reason,
-    bool is_discarded) {
-  // Increment the count in the data store for tabs metrics reporting.
-  tab_stats_data_store_->OnTabDiscardStateChange(reason, is_discarded);
-}
-
-void TabStatsTracker::OnAutoDiscardableStateChange(
-    content::WebContents* contents,
-    bool is_auto_discardable) {}
-
 void TabStatsTracker::OnInterval(
     base::TimeDelta interval,
     TabStatsDataStore::TabsStateDuringIntervalMap* interval_map) {
@@ -381,20 +335,6 @@ void TabStatsTracker::OnInterval(
   tab_stats_data_store_->ResetIntervalData(interval_map);
 }
 
-void TabStatsTracker::OnTabDiscardCountReportInterval() {
-  for (size_t reason = 0;
-       reason < static_cast<size_t>(LifecycleUnitDiscardReason::kMaxValue) + 1;
-       reason++) {
-    base::UmaHistogramCounts100(
-        kTabDiscardCountHistogramNames[reason],
-        tab_stats_data_store_->tab_stats().tab_discard_counts[reason]);
-    base::UmaHistogramCounts100(
-        kTabReloadCountHistogramNames[reason],
-        tab_stats_data_store_->tab_stats().tab_reload_counts[reason]);
-  }
-  tab_stats_data_store_->ClearTabDiscardAndReloadCounts();
-}
-
 void TabStatsTracker::OnInitialOrInsertedTab(
     content::WebContents* web_contents) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

chrome/browser/metrics/tab_stats_tracker.h

@@ -20,8 +20,6 @@
 #include "build/build_config.h"
 #include "chrome/browser/metrics/tab_stats_data_store.h"
 #include "chrome/browser/metrics/tab_stats_tracker_delegate.h"
-#include "chrome/browser/resource_coordinator/lifecycle_unit_state.mojom-forward.h"
-#include "chrome/browser/resource_coordinator/tab_lifecycle_observer.h"
 #include "chrome/browser/ui/browser_list_observer.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
 #include "components/metrics/daily_event.h"
@@ -43,8 +41,7 @@ FORWARD_DECLARE_TEST(TabStatsTrackerBrowserTest,
 //         std::make_unique<TabStatsTracker>(g_browser_process->local_state()));
 class TabStatsTracker : public TabStripModelObserver,
                         public BrowserListObserver,
-                        public base::PowerObserver,
-                        public resource_coordinator::TabLifecycleObserver {
+                        public base::PowerObserver {
  public:
   // Constructor. |pref_service| must outlive this object.
   explicit TabStatsTracker(PrefService* pref_service);
@@ -150,14 +147,6 @@ class TabStatsTracker : public TabStripModelObserver,
   // base::PowerObserver:
   void OnResume() override;
 
-  // resource_coordinator::TabLifecycleObserver:
-  void OnDiscardedStateChange(content::WebContents* contents,
-                              ::mojom::LifecycleUnitDiscardReason reason,
-                              bool is_discarded) override;
-
-  void OnAutoDiscardableStateChange(content::WebContents* contents,
-                                    bool is_auto_discardable) override;
-
   // Callback when an interval timer triggers.
   void OnInterval(base::TimeDelta interval,
                   TabStatsDataStore::TabsStateDuringIntervalMap* interval_map);
@@ -214,17 +203,10 @@ class TabStatsTracker : public TabStripModelObserver,
   // The timer used to report the heartbeat metrics at regular interval.
   base::RepeatingTimer heartbeat_timer_;
 
-  // The timer used to report tab discard and reload count histograms at regular
-  // interval.
-  base::RepeatingTimer tab_discard_reload_stats_timer_;
-
   // The observers that track how the tabs are used.
   std::map<content::WebContents*, std::unique_ptr<WebContentsUsageObserver>>
       web_contents_usage_observers_;
 
-  // Called at regular time intervals to report tab discard count histograms.
-  void OnTabDiscardCountReportInterval();
-
   SEQUENCE_CHECKER(sequence_checker_);
 
   DISALLOW_COPY_AND_ASSIGN(TabStatsTracker);

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -3618,6 +3618,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Discarding.DiscardsPer10Minutes" units="tabs"
     expires_after="M85">
+  <obsolete>
+    Removed 11/2020. Not actively used because reported values are 0 most of the
+    time. It would be more useful to report number of discards per day.
+  </obsolete>
 <!-- Name completed by histogram_suffixes name="DiscardReason" -->
 
   <owner>fdoray@chromium.org</owner>
@@ -3733,6 +3737,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Discarding.ReloadsPer10Minutes" units="tabs"
     expires_after="M85">
+  <obsolete>
+    Removed 11/2020. Not actively used because reported values are 0 most of the
+    time. It would be more useful to report number of reloads per day.
+  </obsolete>
 <!-- Name completed by histogram_suffixes name="DiscardReason" -->
 
   <owner>fdoray@chromium.org</owner>