[remote suggestions] Add a new histogram for recording the time since a snippet was fetched.

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 <cmath>
 #include <string>
 #include <type_traits>
 
@@ skipping 43 matching lines @@
 const char kHistogramMoreButtonShown[] =
     "NewTabPage.ContentSuggestions.MoreButtonShown";
 const char kHistogramMoreButtonClicked[] =
     "NewTabPage.ContentSuggestions.MoreButtonClicked";
 const char kHistogramMovedUpCategoryNewIndex[] =
     "NewTabPage.ContentSuggestions.MovedUpCategoryNewIndex";
 const char kHistogramCategoryDismissed[] =
     "NewTabPage.ContentSuggestions.CategoryDismissed";
 const char kHistogramContentSuggestionsTimeSinceLastBackgroundFetch[] =
     "NewTabPage.ContentSuggestions.TimeSinceLastBackgroundFetch";
+const char kHistogramContentSuggestionsTimeSinceSuggestionFetched[] =

[Marc Treib, 2017/02/21 09:14:09]

optional nit: You could remove "ContentSuggestions" from the variable name, also
from the one above. All the other histograms don't have it, and it's obvious
from context anyway.

[markusheintz_, 2017/02/21 11:31:50]

Done.

+    "NewTabPage.ContentSuggestions.TimeSinceSuggestionFetched";
 
 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 HistogramCategories {
   EXPERIMENTAL,
   RECENT_TABS,
@@ skipping 154 matching lines @@
   UMA_HISTOGRAM_EXACT_LINEAR(kHistogramShown, global_position,
                              kMaxSuggestionsTotal);
   LogCategoryHistogramPosition(kHistogramShown, category, position_in_category,
                                kMaxSuggestionsPerCategory);
 
   base::TimeDelta age = base::Time::Now() - publish_date;
   LogCategoryHistogramAge(kHistogramShownAge, category, age);
 
   LogCategoryHistogramScore(kHistogramShownScore, category, score);
 
+  // Records the time since the fetch time of the displayed snippet.
+  UMA_HISTOGRAM_CUSTOM_TIMES(
+      kHistogramContentSuggestionsTimeSinceSuggestionFetched,
+      base::Time::Now() - fetch_date, base::TimeDelta::FromSeconds(1),
+      base::TimeDelta::FromDays(7),
+      /*bucket_count=*/100);

[Marc Treib, 2017/02/21 09:14:09]

Should we record this only for ARTICLES?
If not, should it be a per-category histogram, and/or should we only record it
if we actually have a fetch date?

[markusheintz_, 2017/02/21 11:31:50]

Done.

No the fetch date for non Article suggestions should always be 0.

+
   // 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) &&
       position_in_category == 0) {
     RecordContentSuggestionsUsage();
 
     // Records the time since the last background fetch of the remote content
     // suggestions.
     UMA_HISTOGRAM_CUSTOM_TIMES(

[jkrcal, 2017/02/20 18:38:37]

I am wondering, do we still need the old histogram?
I do not see the situation when we would need it.

[markusheintz_, 2017/02/21 11:31:50]

I removed the code. 

         kHistogramContentSuggestionsTimeSinceLastBackgroundFetch,
         base::Time::Now() - fetch_date, base::TimeDelta::FromSeconds(1),
         base::TimeDelta::FromDays(7),
         /*bucket_count=*/100);
   }
 }
 
 void OnSuggestionOpened(int global_position,
                         Category category,
                         int category_index,
@@ skipping 93 matching lines @@
 }
 
 void OnCategoryDismissed(Category category) {
   UMA_HISTOGRAM_ENUMERATION(kHistogramCategoryDismissed,
                             GetHistogramCategory(category),
                             HistogramCategories::COUNT);
 }
 
 }  // namespace metrics
 }  // namespace ntp_snippets