[NTP::SectionOrder] Track category index after it has been moved up.

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 b6c26ed20a829597a842ec91da8efffd00c26ef0..38860864bc854b192923f251d5c8419d9b12ad1b 100644
--- a/components/ntp_snippets/content_suggestions_metrics.cc
+++ b/components/ntp_snippets/content_suggestions_metrics.cc
@@ -55,6 +55,8 @@ 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[] =
@@ -330,6 +332,11 @@ void OnSuggestionTargetVisited(Category category, base::TimeDelta visit_time) {
   base::UmaHistogramLongTimes(name, visit_time);
 }
 
+void OnCategoryMovedUp(int new_index) {
+  UMA_HISTOGRAM_EXACT_LINEAR(kHistogramMovedUpCategoryNewIndex, new_index,
+                             kMaxCategories);
+}
+
 void OnMoreButtonShown(Category category, int position) {
   // The "more" card can appear in addition to the actual suggestions, so add
   // one extra bucket to this histogram.