Remove RelatedHistogramSet.

tracing/tracing/value/histogram.html

Index: tracing/tracing/value/histogram.html
diff --git a/tracing/tracing/value/histogram.html b/tracing/tracing/value/histogram.html
index 5d4480bedc04e58a2311f34b19a000eb8d0e0969..278aca112533a61b7a943e6f8d620d8c8873c5d3 100644
--- a/tracing/tracing/value/histogram.html
+++ b/tracing/tracing/value/histogram.html
@@ -576,17 +576,17 @@ tr.exportTo('tr.v', function() {
 
       let mergedFrom = this.diagnostics.get(tr.v.d.RESERVED_NAMES.MERGED_FROM);
       if (!mergedFrom) {
-        mergedFrom = new tr.v.d.RelatedHistogramSet();
+        mergedFrom = new tr.v.d.RelatedHistogramMap();
         this.diagnostics.set(tr.v.d.RESERVED_NAMES.MERGED_FROM, mergedFrom);
       }
-      mergedFrom.add(other);
+      mergedFrom.set(mergedFrom.length, other);
 
       let mergedTo = other.diagnostics.get(tr.v.d.RESERVED_NAMES.MERGED_TO);
       if (!mergedTo) {
-        mergedTo = new tr.v.d.RelatedHistogramSet();
+        mergedTo = new tr.v.d.RelatedHistogramMap();
         other.diagnostics.set(tr.v.d.RESERVED_NAMES.MERGED_TO, mergedTo);
       }
-      mergedTo.add(this);
+      mergedTo.set(mergedTo.length, this);
 
       this.diagnostics.addDiagnostics(other.diagnostics);