Remove RelatedHistogramSet.

tracing/tracing/value/diagnostics/related_histogram_map.html

Index: tracing/tracing/value/diagnostics/related_histogram_map.html
diff --git a/tracing/tracing/value/diagnostics/related_histogram_map.html b/tracing/tracing/value/diagnostics/related_histogram_map.html
index 73fc3ad1d52963cda497d2e624a8737f5630bf5e..08e9bb764d564c5e69cd6ce452398c660e161b99 100644
--- a/tracing/tracing/value/diagnostics/related_histogram_map.html
+++ b/tracing/tracing/value/diagnostics/related_histogram_map.html
@@ -42,13 +42,13 @@ tr.exportTo('tr.v.d', function() {
         RelatedHistogramMap.
 
         otherParentHist -----------------------------> parentHist
-        |               merged to RelatedHistogramSet   |
+        |               merged to RelatedHistogramMap   |
         |                                               |
         | otherDiagnostic                               | this
         | RelatedHistogramMap                           | RelatedHistogramMap
         v                                               v
         otherRelatedHist -----------------------------> relatedHist
-                         merged to RelatedHistogramSet
+                         merged to RelatedHistogramMap
 
         However, |otherRelatedHist| may have been merged to Histograms using
         different grouping keys, so if |relatedHist|'s merge path is different
@@ -64,7 +64,7 @@ tr.exportTo('tr.v.d', function() {
             tr.v.d.RESERVED_NAMES.MERGED_TO);
         if (mergedTo === undefined) continue;
 
-        for (const relatedHist of mergedTo) {
+        for (const relatedHist of mergedTo.histogramsByName_.values()) {
           const relatedGroupingPath = tr.v.d.GroupingPath.getFromHistogram(
               relatedHist);
           if (relatedGroupingPath === undefined) continue;