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

components/ntp_snippets/content_suggestions_metrics.cc

Index: components/ntp_snippets/content_suggestions_metrics.cc
diff --git a/components/ntp_snippets/content_suggestions_metrics.cc b/components/ntp_snippets/content_suggestions_metrics.cc
index 33d61743ca4a5a31b617d7eda8f0842074a26c4f..a7ec471f0725cec946da84abc4dea11e3beb0bd5 100644
--- a/components/ntp_snippets/content_suggestions_metrics.cc
+++ b/components/ntp_snippets/content_suggestions_metrics.cc
@@ -51,6 +51,8 @@ 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";
 
@@ -248,6 +250,7 @@ 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);
@@ -259,11 +262,23 @@ void OnSuggestionShown(int global_position,
 
   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);
   }
 }