Add a histogram for recording content suggestions local usage time stats.

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 22 matching lines @@
     "NewTabPage.ContentSuggestions.OpenDisposition";
 const char kHistogramMenuOpened[] = "NewTabPage.ContentSuggestions.MenuOpened";
 const char kHistogramMenuOpenedAge[] =
     "NewTabPage.ContentSuggestions.MenuOpenedAge";
 const char kHistogramMenuOpenedScore[] =
     "NewTabPage.ContentSuggestions.MenuOpenedScore";
 const char kHistogramDismissedUnvisited[] =
     "NewTabPage.ContentSuggestions.DismissedUnvisited";
 const char kHistogramDismissedVisited[] =
     "NewTabPage.ContentSuggestions.DismissedVisited";
+const char kHistogramUsageTimeLocal[] =
+    "NewTabPage.ContentSuggestions.UsageTimeLocal";
 const char kHistogramVisitDuration[] =
     "NewTabPage.ContentSuggestions.VisitDuration";
 const char kHistogramMoreButtonShown[] =
     "NewTabPage.ContentSuggestions.MoreButtonShown";
 const char kHistogramMoreButtonClicked[] =
     "NewTabPage.ContentSuggestions.MoreButtonClicked";
 
 const char kPerCategoryHistogramFormat[] = "%s.%s";
 
 // Each suffix here should correspond to an entry under histogram suffix
@@ skipping 99 matching lines @@
 }
 
 void LogCategoryHistogramScore(const char* base_name,
                                Category category,
                                float score) {
   std::string name = GetCategoryHistogramName(base_name, category);
   // Since the histogram name is dynamic, we can't use the regular macro.
   UmaHistogramScore(name, score);
 }
 
+// Records ContentSuggestions usage. Therefore the day is sliced into 20min
+// buckets. Depending on the current local time the count of the corresponding
+// bucket is increased.

[Marc Treib, 2016/11/16 14:14:29]

Mention that "usage" means "impression" rather than "click"?

[markusheintz_, 2016/11/16 14:52:13]

It will be more that just the impression, i'll also count how often an article
was opened and other usages. I'll add counting article open events.

[Marc Treib, 2016/11/16 15:10:08]

Then all the more important to define what we consider a "usage" :)

Is impression + click all that will be tracked in this histogram? If not, it'd
probably be best to add everything else in this CL too - it's considered bad
practice to change the definition of a histogram after it's been introduced.

+void RecordContentSuggestionsUsage() {
+  const int kBucketSize = 20;  // min

[Marc Treib, 2016/11/16 14:14:29]

nit: kBucketSizeMins and remove the comment?

[markusheintz_, 2016/11/16 14:52:13]

Done.

+  const int kNumBuckets = 24 * 60 / kBucketSize;
+
+  base::Time now(base::Time::Now());
+  base::Time::Exploded now_exploded;
+  now.LocalExplode(&now_exploded);

[Marc Treib, 2016/11/16 14:14:29]

nit: You could just write
base::Time::Now().LocalExplode(...)

[markusheintz_, 2016/11/16 14:52:13]

Done.

+  size_t bucket = (now_exploded.hour * 60 + now_exploded.minute) / kBucketSize;

[Marc Treib, 2016/11/16 14:14:29]

Why size_t rather than int?

[markusheintz_, 2016/11/16 14:52:13]

bucket size can't be negative.

[Marc Treib, 2016/11/16 15:10:08]

Nothing here can be negative, yet everything else is an int. :)
Per the style guide, we don't use unsigned types simply because the value
shouldn't be negative:
https://google.github.io/styleguide/cppguide.html#Integer_Types

+
+  UMA_HISTOGRAM_ENUMERATION(
+       kHistogramUsageTimeLocal,
+       bucket,
+       kNumBuckets);

[Marc Treib, 2016/11/16 14:14:29]

nit: run "git cl format"

[markusheintz_, 2016/11/16 14:52:13]

Done.

+}
+
 }  // namespace
 
 void OnPageShown(
     const std::vector<std::pair<Category, int>>& suggestions_per_category) {
   int suggestions_total = 0;
   for (const std::pair<Category, int>& item : suggestions_per_category) {
     LogCategoryHistogramEnumeration(kHistogramCountOnNtpOpened, item.first,
                                     item.second, kMaxSuggestionsPerCategory);
     suggestions_total += item.second;
   }
 
   UMA_HISTOGRAM_ENUMERATION(kHistogramCountOnNtpOpened, suggestions_total,
                             kMaxSuggestionsTotal);
 }
 
 void OnSuggestionShown(int global_position,
                        Category category,
                        int category_position,
                        base::Time publish_date,
                        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);
+
+  // When the first suggestion of all snippets is shown, then we count this as a

[Marc Treib, 2016/11/16 14:14:29]

"When the first of all suggestions is shown, ..."? Let's try not to use
"snippet" anymore.

[markusheintz_, 2016/11/16 14:52:13]

Done.

+  // single usage of content suggestions.
+  // TODO(markusheintz): Use position 0 once http://crbug.com/664539 is fixed.

[Marc Treib, 2016/11/16 14:14:29]

It'll be fixed very soon, see https://codereview.chromium.org/2504963002, so
please use 0 already :)

[markusheintz_, 2016/11/16 14:52:13]

Done.

+  if (global_position == 1) {
+    RecordContentSuggestionsUsage();
+  }
 }
 
 void OnSuggestionOpened(int global_position,
                         Category category,
                         int category_position,
                         base::Time publish_date,
                         float score,
                         WindowOpenDisposition disposition) {
   UMA_HISTOGRAM_ENUMERATION(kHistogramOpened, global_position,
                             kMaxSuggestionsTotal);
@@ skipping 62 matching lines @@
 
 void OnMoreButtonClicked(Category category, int position) {
   // The "more" card can appear in addition to the actual suggestions, so add
   // one extra bucket to this histogram.
   LogCategoryHistogramEnumeration(kHistogramMoreButtonClicked, category,
                                   position, kMaxSuggestionsPerCategory + 1);
 }
 
 }  // namespace metrics
 }  // namespace ntp_snippets