[Zine] Add a metric to record number of visible sections on NTP.

components/ntp_snippets/content_suggestions_metrics.h

 // 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.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_METRICS_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_METRICS_H_
 
 #include <utility>
 #include <vector>
 
 #include "base/time/time.h"
 #include "components/ntp_snippets/category.h"
 #include "ui/base/window_open_disposition.h"
 
 namespace ntp_snippets {
 namespace metrics {
 
 void OnPageShown(
-    const std::vector<std::pair<Category, int>>& suggestions_per_category);
+    const std::vector<std::pair<Category, int>>& suggestions_per_category,
+    int visible_categories_count);
 
 // Should only be called once per NTP for each suggestion.
 void OnSuggestionShown(int global_position,
                        Category category,
                        int position_in_category,
                        base::Time publish_date,
                        float score,
                        base::Time fetch_date);
 
 // TODO(crbug.com/682160): Take struct, so that one could not mix up the
@@ skipping 33 matching lines @@
 void RecordContentSuggestionDismissed();
 
 void RecordCategoryDismissed();
 
 void RecordFetchAction();
 
 }  // namespace metrics
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_SERVICE_H_