[telemetry] Fix type of of media metric.

tools/perf/metrics/media.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file contains common utilities to find video/audio elements on a page
 // and collect metrics for each.
 
 (function() {
   // MediaMetric class responsible for collecting metrics on a media element.
   // It attaches required event listeners in order to collect different metrics.
@@ skipping 78 matching lines @@
   };
 
   HTMLMediaMetric.prototype.onWillLoop = function(e) {
     var loopTimer = new Timer();
     var metric = this;
     var loopCount = e.loopCount;
     var onEndLoop = function(e) {
         var actualDuration = loopTimer.stop();
         var idealDuration = metric.element.duration * loopCount;
         var avg_loop_time = (actualDuration - idealDuration) / loopCount;
-        metric.metrics['avg_loop_time'] = avg_loop_time.toFixed(3);
+        metric.metrics['avg_loop_time'] =
+            Math.round(avg_loop_time * 1000) / 1000;
         e.target.removeEventListener('endLoop', onEndLoop);
       };
     this.element.addEventListener('endLoop', onEndLoop);
   };
 
   HTMLMediaMetric.prototype.appendMetric = function(metric, value) {
     if (!this.metrics[metric])
       this.metrics[metric] = [];
     this.metrics[metric].push(value);
   }
@@ skipping 90 matching lines @@
       metrics.push(window.__mediaMetrics[i].getSummary());
     return metrics;
   }
 
   window.__globalCounter = 0;
   window.__mediaMetrics = [];
   window.__getMediaMetric = getMediaMetric;
   window.__getAllMetrics = getAllMetrics;
   window.__createMediaMetricsForDocument = createMediaMetricsForDocument;
 })();