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.
+
+// Define a variable called willPlay which indicates if the media is expected
+// to start playing during the test.
+
+var canPlaySeen = false;
+var playingSeen = false;
+var canPlayThroughSeen = false;
+var hasError = false;
+
+var mediaEl = document.getElementById("mediaEl");
+
+function mediaEventHandler(e) {
+  console.log(e.type);
+
+  switch (e.type) {
+    case 'canplay':
+      canPlaySeen = true;
+      break;
+    case 'playing':
+      playingSeen = true;
+      break;
+    case 'canplaythrough':
+      canPlayThroughSeen = true;
+      break;
+    case 'error':
+      hasError = true;
+      break;
+  }
+
+  if ((willPlay && canPlayThroughSeen && playingSeen) ||
+      (!willPlay && canPlayThroughSeen && !playingSeen)) {
+    document.title = 'PASS';
+  }
+}
+
+mediaEl.addEventListener('playing', mediaEventHandler, false);
+mediaEl.addEventListener('canplay', mediaEventHandler, false);
+mediaEl.addEventListener('canplaythrough', mediaEventHandler, false);
+mediaEl.addEventListener('error', 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;
+}