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 sleep(millis) {
+  var date = new Date();
+  var curDate = null;
+  do {
+    curDate = new Date();
+  } while(curDate - date < millis);
+}
+
+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;
+  }
+
+  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);
+
+if (testNetworkEvents) {
+  mediaEl.addEventListener('stalled', mediaEventHandler, false);
+  mediaEl.addEventListener('loadstart', mediaEventHandler, false);
+}
+
+function DidPrerenderPass() {
+  if (testNetworkEvents)
+    sleep(5000);  // Stalled happens after 3000 ms.

[scherkus (not reviewing), 2011/11/23 01:43:31]

there's no way to signal when the test has completed?

this seems really unfortunate!

[Shishir, 2011/11/23 01:48:37]

akaik the stalled event is fired when there is no progress for 3 seconds.  The
event seems to be fired on the renderer side and the browser doenst know about
it. 

[scherkus (not reviewing), 2011/12/01 05:38:13]

Yeah I don't really know how prerender tests work -- when/how is this function
invoked? There's no way to signal to the browser somehow that the test completed
at all?

For example what's the TitleWatcher stuff?  Could that be used at all?

+
+  // The media should not have started at this point.
+  return !canPlaySeen && !playingSeen && !hasError &&
+      mediaEl.currentTime == 0 &&
+      mediaEl.readyState == mediaEl.HAVE_NOTHING &&
+      (!testNetworkEvents || (loadStartSeen && stalledSeen));
+}
+
+function DidDisplayPass() {
+  // The actual test is done via the TitleWatcher.
+  return true;
+}