Add Telemetry media loop action.

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 7cef7cd0c74ce2794cc298b611dd176a6b397d07..8cd3dc23e0048820f5b3ad950aeeabb374fb95fe 100644
--- a/tools/perf/metrics/media.js
+++ b/tools/perf/metrics/media.js
@@ -54,6 +54,9 @@
     this.element.addEventListener('willSeek', function (e) {
         metric.onWillSeek(e);
       }, false);
+    this.element.addEventListener('willLoop', function (e) {
+        metric.onWillLoop(e);
+      }, false);
   }
 
   HTMLMediaMetric.prototype = new MediaMetricBase();
@@ -85,6 +88,20 @@
     this.element.addEventListener('seeked', onSeeked);
   };
 
+  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);
+        e.target.removeEventListener('endLoop', onEndLoop);
+      };
+    this.element.addEventListener('endLoop', onEndLoop);
+  };
+
   HTMLMediaMetric.prototype.appendMetric = function(metric, value) {
     if (!this.metrics[metric])
       this.metrics[metric] = [];