Convert chart-json to Histograms.

tracing/tracing/results2_template.html

Index: tracing/tracing/results2_template.html
diff --git a/tracing/tracing/results2_template.html b/tracing/tracing/results2_template.html
index 2751afb9ad094cd966b3805dd1c6ae9294505b68..a651b3373770e238390d895ac9cd8cf3b3242505 100644
--- a/tracing/tracing/results2_template.html
+++ b/tracing/tracing/results2_template.html
@@ -105,7 +105,6 @@ class HistogramImporter {
 
   removeJsonDivs_() {
     document.body.removeChild(this.jsonDivs_[0].parentNode);
-    delete this.jsonDivs_;
   }
 }
 
@@ -113,6 +112,9 @@ var importer = new HistogramImporter();
 
 document.addEventListener('DOMContentLoaded', () => {
   importer.importHistograms();
+
+  // Free the objects and DOM referenced by the importer.
+  importer = undefined;
 });
 
 })();