[Feed] Emit time since last fetch when fetch time is cleared.

Bug: 908963
Change-Id: I655419255ea7a99e3d053fba85464f0ce082ddfe
Reviewed-on: https://chromium-review.googlesource.com/c/1395137Reviewed-by: Filip Gorski <fgorski@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619876}

components/feed/core/feed_scheduler_host.cc

@@ -317,6 +317,14 @@ void FeedSchedulerHost::OnSuggestionsShown() {
 }
 
 void FeedSchedulerHost::OnArticlesCleared(bool suppress_refreshes) {
+  base::TimeDelta attempt_age =
+      clock_->Now() - profile_prefs_->GetTime(prefs::kLastFetchAttemptTime);
+  UMA_HISTOGRAM_CUSTOM_TIMES(
+      "ContentSuggestions.Feed.Scheduler.TimeSinceLastFetchOnClear",
+      attempt_age, base::TimeDelta::FromSeconds(1),
+      base::TimeDelta::FromDays(7),
+      /*bucket_count=*/50);
+
   // Since there are no stored articles, a refresh will be needed soon.
   profile_prefs_->ClearPref(prefs::kLastFetchAttemptTime);
 

components/ntp_snippets/remote/remote_suggestions_scheduler_impl.cc

@@ -887,6 +887,16 @@ void RemoteSuggestionsSchedulerImpl::OnFetchCompleted(Status fetch_status) {
 }
 
 void RemoteSuggestionsSchedulerImpl::ClearLastFetchAttemptTime() {
+  // Added during Feed rollout to help investigate https://crbug.com/908963.
+  base::TimeDelta attempt_age =
+      clock_->Now() -
+      profile_prefs_->GetTime(prefs::kSnippetLastFetchAttemptTime);
+  UMA_HISTOGRAM_CUSTOM_TIMES(
+      "ContentSuggestions.Feed.Scheduler.TimeSinceLastFetchOnClear",
+      attempt_age, base::TimeDelta::FromSeconds(1),
+      base::TimeDelta::FromDays(7),
+      /*bucket_count=*/50);
+
   profile_prefs_->ClearPref(prefs::kSnippetLastFetchAttemptTime);
   // To mark the last fetch as stale, we need to keep the time in prefs, only
   // making sure it is long ago.

tools/metrics/histograms/histograms.xml

@@ -16725,6 +16725,18 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="ContentSuggestions.Feed.Scheduler.TimeSinceLastFetchOnClear"
+    units="ms" expires_after="2019-10-01">
+  <owner>skym@chromium.org</owner>
+  <owner>fgorski@chromium.org</owner>
+  <summary>
+    When the previous last fetch attempt time is cleared, log the time since the
+    last fetch attempt. This typically occurs when suggestions are cleared. A
+    client that has never made a successful fetch (at least since it was last
+    cleared) will report the time since epoch.
+  </summary>
+</histogram>
+
 <histogram name="ContentSuggestions.Feed.TokenFetchStatus"
     enum="GoogleServiceAuthError">
   <obsolete>