[NTPSnippets] Records the time since last successful bg fetch.

components/ntp_snippets/content_suggestions_metrics.cc

 // Copyright 2016 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 "components/ntp_snippets/content_suggestions_metrics.h"
 
 #include <string>
 #include <type_traits>
 
 #include "base/metrics/histogram.h"
@@ skipping 33 matching lines @@
 const char kHistogramArticlesUsageTimeLocal[] =
     "NewTabPage.ContentSuggestions.UsageTimeLocal";
 const char kHistogramVisitDuration[] =
     "NewTabPage.ContentSuggestions.VisitDuration";
 const char kHistogramMoreButtonShown[] =
     "NewTabPage.ContentSuggestions.MoreButtonShown";
 const char kHistogramMoreButtonClicked[] =
     "NewTabPage.ContentSuggestions.MoreButtonClicked";
 const char kHistogramCategoryDismissed[] =
     "NewTabPage.ContentSuggestions.CategoryDismissed";
+const char kHistogramContentSuggestionsTimeSinceLastBackgroundFetch[] =
+    "NewTabPage.ContentSuggestions.TimeSinceLastBackgroundFetch";
 
 const char kPerCategoryHistogramFormat[] = "%s.%s";
 
 // This mostly corresponds to the KnownCategories enum, but it is contiguous
 // and contains exactly the values to be recorded in UMA. Don't remove or
 // reorder elements, only add new ones at the end (before COUNT), and keep in
 // sync with ContentSuggestionsCategory in histograms.xml.
 enum class HistogramCategories {
   EXPERIMENTAL,
   RECENT_TABS,
@@ skipping 177 matching lines @@
   }
 
   UMA_HISTOGRAM_ENUMERATION(kHistogramCountOnNtpOpened, suggestions_total,
                             kMaxSuggestionsTotal);
 }
 
 void OnSuggestionShown(int global_position,
                        Category category,
                        int category_position,
                        base::Time publish_date,
+                       base::Time last_background_fetch_time,
                        float score) {
   UMA_HISTOGRAM_ENUMERATION(kHistogramShown, global_position,
                             kMaxSuggestionsTotal);
   LogCategoryHistogramEnumeration(kHistogramShown, category, category_position,
                                   kMaxSuggestionsPerCategory);
 
   base::TimeDelta age = base::Time::Now() - publish_date;
   LogCategoryHistogramAge(kHistogramShownAge, category, age);
 
   LogCategoryHistogramScore(kHistogramShownScore, category, score);
 
+  // TODO(markusheintz): Discuss whether the code below should be move into a
+  // separate method called OnSuggestionsListShown.
   // When the first of the articles suggestions is shown, then we count this as
   // a single usage of content suggestions.
   if (category.IsKnownCategory(KnownCategories::ARTICLES) &&
       category_position == 0) {
     RecordContentSuggestionsUsage();
+
+    // Records the time since the last background fetch of the remote content
+    // suggestions.
+    UMA_HISTOGRAM_CUSTOM_TIMES(
+        kHistogramContentSuggestionsTimeSinceLastBackgroundFetch,
+        base::Time::Now() - last_background_fetch_time,
+        base::TimeDelta::FromSeconds(1), base::TimeDelta::FromDays(3),

[Marc Treib, 2016/12/15 12:47:22]

Should we make the max a bit bigger, to also capture "bad" cases where no
background fetch has happened for a while?

+        /*bucket_count=*/100);
   }
 }
 
 void OnSuggestionOpened(int global_position,
                         Category category,
                         int category_position,
                         base::Time publish_date,
                         float score,
                         WindowOpenDisposition disposition) {
   UMA_HISTOGRAM_ENUMERATION(kHistogramOpened, global_position,
@@ skipping 73 matching lines @@
 }
 
 void OnCategoryDismissed(Category category) {
   UMA_HISTOGRAM_ENUMERATION(kHistogramCategoryDismissed,
                             static_cast<int>(GetHistogramCategory(category)),
                             static_cast<int>(HistogramCategories::COUNT));
 }
 
 }  // namespace metrics
 }  // namespace ntp_snippets