[telemetry] Fix type of of media metric.

tools/perf/metrics/media.js

Index: tools/perf/metrics/media.js
diff --git a/tools/perf/metrics/media.js b/tools/perf/metrics/media.js
index 4df38d1a6ee5df7729734de74a2388a959f0d78f..85b10526da5988e61385fc059a371383eb65b982 100644
--- a/tools/perf/metrics/media.js
+++ b/tools/perf/metrics/media.js
@@ -96,7 +96,8 @@
         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);