Refactor NumericBuilder to HistogramBinBoundaries.

tracing/tracing/metrics/system_health/long_tasks_metric.html

Index: tracing/tracing/metrics/system_health/long_tasks_metric.html
diff --git a/tracing/tracing/metrics/system_health/long_tasks_metric.html b/tracing/tracing/metrics/system_health/long_tasks_metric.html
index 9782488bd5fe90fad9135de4b38370d3f716f9a2..d12818d50d6f1cbf53b5b779de00cc74ad388d19 100644
--- a/tracing/tracing/metrics/system_health/long_tasks_metric.html
+++ b/tracing/tracing/metrics/system_health/long_tasks_metric.html
@@ -22,9 +22,6 @@ tr.exportTo('tr.metrics.sh', function() {
   // uninteresting.
   var LONGEST_TASK_MS = 1000;
 
-  var timeDurationInMs_smallerIsBetter =
-    tr.v.Unit.byName.timeDurationInMs_smallerIsBetter;
-
   /**
    * This helper function calls |cb| for each of the top-level tasks on the
    * given thread in the given range whose duration is longer than LONG_TASK_MS.
@@ -67,18 +64,6 @@ tr.exportTo('tr.metrics.sh', function() {
         });
   }
 
-  var LONG_TASK_NUMERIC_BUILDER = tr.v.NumericBuilder.createLinear(
-      tr.v.Unit.byName.timeDurationInMs_smallerIsBetter,
-      tr.b.Range.fromExplicitRange(LONG_TASK_MS, LONGEST_TASK_MS), 50);
-
-  // This range spans several orders of magnitude, and the data is likely to
-  // form an exponential distribution, so use exponential bins in order to
-  // prevent the lowest bin from containing almost all of the samples.
-  // See also most UMA histograms that are exponential for similar reasons.
-  var SLICE_NUMERIC_BUILDER = tr.v.NumericBuilder.createExponential(
-      tr.v.Unit.byName.timeDurationInMs_smallerIsBetter,
-      tr.b.Range.fromExplicitRange(0.1, LONGEST_TASK_MS), 50);
-
   /**
    * This metric directly measures long tasks on renderer main threads.
    * This metric requires only the 'toplevel' tracing category.
@@ -89,7 +74,10 @@ tr.exportTo('tr.metrics.sh', function() {
    */
   function longTasksMetric(values, model, opt_options) {
     var rangeOfInterest = opt_options ? opt_options.rangeOfInterest : undefined;
-    var longTaskNumeric = LONG_TASK_NUMERIC_BUILDER.build();
+    var longTaskNumeric = new
+      tr.v.Histogram(tr.v.Unit.byName.timeDurationInMs_smallerIsBetter,
+          tr.v.HistogramBinBoundaries.createLinear(
+              LONG_TASK_MS, LONGEST_TASK_MS, 40));
     var slices = new tr.model.EventSet();
     iterateRendererMainThreads(model, function(thread) {
       iterateLongTopLevelTasksOnThreadInRange(
@@ -104,9 +92,13 @@ tr.exportTo('tr.metrics.sh', function() {
     var longTaskValue = new tr.v.NumericValue(
         'long tasks', longTaskNumeric, options);
     values.addValue(longTaskValue);
+
+    var sampleForEvent = undefined;
     var composition = tr.v.d.Composition.buildFromEvents(
-        values, 'long tasks ', slices, SLICE_NUMERIC_BUILDER,
-        e => (model.getUserFriendlyCategoryFromEvent(e) || 'unknown'));
+        values, 'long tasks ', slices,
+        e => (model.getUserFriendlyCategoryFromEvent(e) || 'unknown'),
+        tr.v.Unit.byName.timeDurationInMs_smallerIsBetter, sampleForEvent,
+        tr.v.HistogramBinBoundaries.createExponential(1, LONGEST_TASK_MS, 40));
     composition.colorScheme =
       tr.v.d.COLOR_SCHEME_CHROME_USER_FRIENDLY_CATEGORY_DRIVER;
     longTaskValue.diagnostics.set('category', composition);