Refactor NumericBuilder to HistogramBinBoundaries.

trace_processor/experimental/mappers/trace_stats.html

Index: trace_processor/experimental/mappers/trace_stats.html
diff --git a/trace_processor/experimental/mappers/trace_stats.html b/trace_processor/experimental/mappers/trace_stats.html
index 2af90f8cc43a38d80b817a84b995e272d62199d1..5133dc3321529117517b25b3d6298f07b94ef4f5 100644
--- a/trace_processor/experimental/mappers/trace_stats.html
+++ b/trace_processor/experimental/mappers/trace_stats.html
@@ -14,9 +14,7 @@ found in the LICENSE file.
 'use strict';
 
 tr.exportTo('pi.m', function() {
-  var COUNT_NUMERIC_BUILDER = tr.v.NumericBuilder.createLinear(
-      tr.v.Unit.byName.unitlessNumber, tr.b.Range.fromExplicitRange(0, 50000),
-      20);
+  var COUNT_BOUNDARIES = tr.v.HistogramBinBoundaries.createLinear(0, 5e4, 20);
 
   function traceStatsFunction(result, model) {
     var canonicalUrl = model.canonicalUrl;
@@ -47,7 +45,8 @@ tr.exportTo('pi.m', function() {
       seconds_counts[second]++;
     }
 
-    var histogram = COUNT_NUMERIC_BUILDER.build();
+    var histogram = new tr.v.Histogram(
+        tr.v.Unit.byName.count, COUNT_BOUNDARIES);
 
     for (var second in seconds_counts)
       histogram.add(seconds_counts[second]);