[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 kHistogramContentSuggestionsBackgroundFetchAge[] =
+    "NewTabPage.ContentSuggestions.BackgroundFetchAge";

[Marc Treib, 2016/12/15 10:16:41]

nit: I'm not super happy with the term "Age" here - it's really just the time
since the last background fetch. So how about ".TimeSinceLastBackgroundFetch"?

[markusheintz_, 2016/12/15 12:42:07]

Excellent name suggestion!! I find it much better than mine. Thanks a lot!

 
 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 age of the remote content suggestion based on the last
+    // background fetch time. This is different from the actual content age as

[Marc Treib, 2016/12/15 10:16:41]

Also here: It's not the age of the suggestion, it's the time since the last
fetch. This particular suggestion might potentially even be from an earlier
fetch (if you discarded all newer suggestions, or if the latest fetch didn't
return anything), or it might be from a newer foreground fetch.

[markusheintz_, 2016/12/15 12:42:07]

That's what I describe in the comment. I simplified and shortened to comment to
make it more clear and be more consistent with the new naming.

+    // it records the time span between fetching the suggestions and viewing
+    // them.
+    UMA_HISTOGRAM_CUSTOM_TIMES(kHistogramContentSuggestionsBackgroundFetchAge,
+                               base::Time::Now() - last_background_fetch_time,
+                               base::TimeDelta::FromSeconds(1),
+                               base::TimeDelta::FromDays(3),
+                               /*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