Defer loading of audio/video tags while prerendering.

chrome/test/data/prerender/prerender_html5_common.js

+// Copyright (c) 2011 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.
+
+// Common js for the HTML5_* tests. The following variables need to be defined
+// before this js is included:
+//   - 'willPlay' - indicates if the media is expected to start playing during
+//      the test.
+//   - 'testNetworkEvents' - if set to true, the test will test for the
+//     loadstart and stalled events. NOTE that since the loadstart event fires
+//     very early, to test for it reliably, the source of the media tag
+//     should be added after this script is included or add
+//     'onLoadStart=mediEventHandler' as an attribute to the media element.
+
+function assert(bool) {
+  if (!bool)
+    throw new Error('Assert Failed.');
+}
+
+var canPlaySeen = false;
+var playingSeen = false;
+var canPlayThroughSeen = false;
+var stalledSeen = false;
+var loadStartSeen = false;
+var hasError = false;
+
+assert(typeof(willPlay) != 'undefined');
+assert(typeof(testNetworkEvents) != 'undefined');
+
+var mediaEl = document.getElementById("mediaEl");
+
+function mediaEventHandler(e) {
+  switch (e.type) {
+    case 'canplay':
+      canPlaySeen = true;
+      break;
+    case 'playing':
+      assert(canPlaySeen);
+      playingSeen = true;
+      break;
+    case 'canplaythrough':
+      assert(canPlaySeen);
+      canPlayThroughSeen = true;
+      break;
+    case 'error':
+      hasError = true;
+      break;
+    case 'loadstart':
+      loadStartSeen = true;
+      break;
+    case 'stalled':
+      assert(loadStartSeen);
+      stalledSeen = true;
+      break;
+  }
+
+  var stallDone = !testNetworkEvents || stalledSeen;
+  var progressDone = (willPlay && canPlayThroughSeen && playingSeen) ||
+      (!willPlay && canPlayThroughSeen && !playingSeen);
+
+  if (stallDone && progressDone)
+    document.title = 'PASS';
+}
+
+mediaEl.addEventListener('playing', mediaEventHandler, false);
+mediaEl.addEventListener('canplay', mediaEventHandler, false);
+mediaEl.addEventListener('canplaythrough', mediaEventHandler, false);
+mediaEl.addEventListener('error', mediaEventHandler, false);
+
+if (testNetworkEvents) {
+  mediaEl.addEventListener('stalled', mediaEventHandler, false);
+  mediaEl.addEventListener('loadstart', mediaEventHandler, false);
+}
+
+function DidPrerenderPass() {
+  // The media should not have started at this point.
+  return !canPlaySeen && !playingSeen && !hasError &&
+      mediaEl.currentTime == 0 &&
+      mediaEl.readyState == mediaEl.HAVE_NOTHING;
+}
+
+function DidDisplayPass() {
+  // The actual test is done via the TitleWatcher.
+  return true;
+}