Defer loading of audio/video tags while prerendering.

chrome/renderer/prerender/prerender_webmediaplayer.cc

Index: chrome/renderer/prerender/prerender_webmediaplayer.cc
diff --git a/chrome/renderer/prerender/prerender_webmediaplayer.cc b/chrome/renderer/prerender/prerender_webmediaplayer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..29a2a44eb47e0fcb31e5d12e37f7af6de8c360ac
--- /dev/null
+++ b/chrome/renderer/prerender/prerender_webmediaplayer.cc
@@ -0,0 +1,73 @@
+// 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.
+
+#include "chrome/renderer/prerender/prerender_webmediaplayer.h"
+
+#include "chrome/common/render_messages.h"
+#include "content/public/renderer/render_view.h"
+#include "media/base/filter_collection.h"
+#include "media/base/media_log.h"
+#include "media/base/pipeline_impl.h"
+#include "third_party/WebKit/Source/WebKit/chromium/public/WebURL.h"
+#include "webkit/glue/webmediaplayer_delegate.h"
+
+namespace prerender {
+
+PrerenderWebMediaPlayer::PrerenderWebMediaPlayer(
+    content::RenderView* render_view,
+    WebKit::WebMediaPlayerClient* client,
+    base::WeakPtr<webkit_glue::WebMediaPlayerDelegate> delegate,
+    media::FilterCollection* collection,
+    media::MessageLoopFactory* message_loop_factory,
+    webkit_glue::MediaStreamClient* media_stream_client,
+    media::MediaLog* media_log)
+    : RenderViewObserver(render_view),
+      WebMediaPlayerImpl(client,
+                         delegate,
+                         collection,
+                         message_loop_factory,
+                         media_stream_client,
+                         media_log),
+      is_prerendering_(true) {
+}
+
+PrerenderWebMediaPlayer::~PrerenderWebMediaPlayer() {}
+
+void PrerenderWebMediaPlayer::load(const WebKit::WebURL& url) {
+  if (is_prerendering_) {
+    url_to_load_.reset(new WebKit::WebURL(url));

[cbentzel, 2011/11/15 18:55:33]

Will this ever get called multiple times if the media element has multiple child
<source elements>? 

I'm reading through
http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#media-...
and it looks like the resource algorithm will go through the sources serially,
but I just want to confirm.

[scherkus (not reviewing), 2011/11/16 02:02:23]

AFAIK load() is only called once per lifetime -- in other words a new media
player object is created if the source changes

it would be good to codify this with a CHECK()

[Shishir, 2011/11/17 21:18:49]

Verified that a second load form js causes a new media player to be created. So
adding a dcheck.
I am unable to test with a double load because the destructor of the first media
player causes the test to hang. Probably has to do with
WebMediaPlayerImpl::Destroy() call. Verfied that it doesnt hang on a test page
using the browser.

+    return;
+  }
+  WebMediaPlayerImpl::load(url);

[cbentzel, 2011/11/15 18:55:33]

Will the "stalled" event get triggered here, or will that not happen since the
load isn't even initiated? 

[scherkus (not reviewing), 2011/11/16 02:02:23]

I believe that's the case -- would be good to use some tests here :)

cbentzel: do you think that's an issue?

in combination with page visibility API it might be OK

[Shishir, 2011/11/17 21:18:49]

This is no necessarily true. The stalled event is fired if there is no progress
for 3 seconds. Some tests last long enough that they are fired and for some they
are not. In either case, I think if the script waits for the canplay event to
fire before interacting with the media or uses page visibility we should be
fine. The stalled event may / may not fire.

+}
+
+void PrerenderWebMediaPlayer::cancelLoad() {
+  if (is_prerendering_) {
+    url_to_load_.reset(NULL);
+    return;
+  }
+  WebMediaPlayerImpl::cancelLoad();
+}
+
+bool PrerenderWebMediaPlayer::OnMessageReceived(const IPC::Message& message) {
+  IPC_BEGIN_MESSAGE_MAP(PrerenderWebMediaPlayer, message)
+    IPC_MESSAGE_HANDLER(ChromeViewMsg_SetIsPrerendering, OnSetIsPrerendering)
+  IPC_END_MESSAGE_MAP()
+
+  return false;
+}
+
+void PrerenderWebMediaPlayer::OnSetIsPrerendering(bool is_prerendering) {
+  // Prerendering can only be enabled prior to a RenderView's first
+  // navigation, so no PrerenderWebMediaPlayer should see the notification
+  // that enables prerendering.
+  DCHECK(!is_prerendering);
+  if (is_prerendering_ && !is_prerendering) {
+    is_prerendering_ = false;
+    if (url_to_load_.get())
+      load(*url_to_load_);
+  }
+}
+
+} // namespace prerender