Generalize delta statistics in Histogram.

tracing/tracing/value/csv_builder.html

Index: tracing/tracing/value/csv_builder.html
diff --git a/tracing/tracing/value/csv_builder.html b/tracing/tracing/value/csv_builder.html
index b9ae96845374e065a46aa7b3e84c23d3f0afef28..45a3377a145e02faf86bc87dce2ea0974018f219 100644
--- a/tracing/tracing/value/csv_builder.html
+++ b/tracing/tracing/value/csv_builder.html
@@ -69,14 +69,8 @@ tr.exportTo('tr.v', function() {
 
     prepare_() {
       for (let hist of this.histograms_) {
-        for (let [name, option] of hist.summaryOptions) {
-          if (name === 'percentile') {
-            for (let percent of option) {
-              this.statisticsNames_.add('pct_' + tr.v.percentToString(percent));
-            }
-          } else if (option) {
-            this.statisticsNames_.add(name);
-          }
+        for (const name of hist.statisticsNames) {
+          this.statisticsNames_.add(name);
         }
 
         let iteration = tr.v.d.TelemetryInfo.getFromHistogram(hist);