Add Telemetry media loop action.

tools/telemetry/telemetry/page/actions/loop.js

Index: tools/telemetry/telemetry/page/actions/loop.js
diff --git a/tools/telemetry/telemetry/page/actions/loop.js b/tools/telemetry/telemetry/page/actions/loop.js
new file mode 100644
index 0000000000000000000000000000000000000000..00ab8d73ec66983d9eb296ed4c430f810f18097b
--- /dev/null
+++ b/tools/telemetry/telemetry/page/actions/loop.js
@@ -0,0 +1,57 @@
+// 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 performs actions on media elements.
+(function() {
+  function loopMedia(selector, loopCount) {
+    // Loops media playback `loopCount` times.
+    var mediaElements = window.__findMediaElements(selector);
+    for (var i = 0; i < mediaElements.length; i++) {
+      loop(mediaElements[i], loopCount);
+    }
+  }
+
+  function loop(element, loopCount) {
+    if (element instanceof HTMLMediaElement)
+      loopHTML5Element(element, loopCount);
+    else
+      throw new Error('Can not play non HTML5 media elements.');
+  }
+
+  function loopHTML5Element(element, loopCount) {
+    element['loop_completed'] = false;
+    var currentLoop = 0;
+    var onLoop = function(e) {
+      ++currentLoop;
+      if (currentLoop == loopCount) {
+        element.pause();
+        element.removeEventListener('seeked', onLoop);
+        element['loop_completed'] = true;
+        // Dispatch endLoopEvent to mark end of looping.
+        var endLoopEvent = document.createEvent('Event');
+        endLoopEvent.initEvent('endLoop', false, false);
+        element.dispatchEvent(endLoopEvent);
+      }
+    };
+
+    function onError(e) {
+      throw new Error('Error playing media :' + e.type);
+    }
+    element.addEventListener('error', onError);
+    element.addEventListener('abort', onError);
+    element.addEventListener('seeked', onLoop);
+    element.loop = true;
+
+    // Dispatch willLoopEvent to measure loop time.
+    var willLoopEvent = document.createEvent('Event');
+    willLoopEvent.initEvent('willLoop', false, false);
+    willLoopEvent.loopCount = loopCount;
+    element.dispatchEvent(willLoopEvent);
+    // Reset HTML5 player to start playback from beginning.
+    element.load();
+    element.play();
+  }
+
+  window.__loopMedia = loopMedia;
+})();