Add stub for assigning media session to media elements

Source/modules/mediasession/HTMLMediaElementMediaSession.cpp

+// Copyright 2015 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 "config.h"
+#include "modules/mediasession/HTMLMediaElementMediaSession.h"
+
+namespace blink {
+
+MediaSession* HTMLMediaElementMediaSession::session(HTMLMediaElement& mediaElement)
+{
+    HTMLMediaElementMediaSession& thisElement = HTMLMediaElementMediaSession::from(mediaElement);

[philipj_slow, 2015/07/02 08:53:15]

This is as in modules/encryptedmedia, but thisElement isnt' actually an element.
Maybe "supplement"? Not perfect, but at least short and accurate.

For the getter I think it would be worthwhile to avoid creating the supplement
if it's not already there and instead just return null.

The Fullscreen supplement has a fromIfExists that is used in some similar
situations.

[davve, 2015/07/02 12:15:44]

fromIfExists seems like a good addition. Done.

+    return thisElement.m_session.get();
+}
+
+void HTMLMediaElementMediaSession::setSession(HTMLMediaElement& mediaElement, MediaSession* session)
+{
+    HTMLMediaElementMediaSession& thisElement = HTMLMediaElementMediaSession::from(mediaElement);

[philipj_slow, 2015/07/02 08:53:15]

from() doesn't need the prefix, so in the cases a one-liner would do:
from(mediaElement).m_session = session; 

[davve, 2015/07/02 12:15:44]

Done.

+    thisElement.m_session = session;
+}
+
+const char* HTMLMediaElementMediaSession::supplementName()
+{
+    return "HTMLMediaElementMediaSession";
+}
+
+HTMLMediaElementMediaSession& HTMLMediaElementMediaSession::from(HTMLMediaElement& element)
+{
+    HTMLMediaElementMediaSession* supplement = static_cast<HTMLMediaElementMediaSession*>(WillBeHeapSupplement<HTMLMediaElement>::from(element, supplementName()));

[philipj_slow, 2015/07/02 08:53:15]

As in the Fullscreen code, this will be able to use fromIfExists.

[davve, 2015/07/02 12:15:44]

Done.

+    if (!supplement) {
+        supplement = new HTMLMediaElementMediaSession();
+        provideTo(element, supplementName(), adoptPtrWillBeNoop(supplement));
+    }
+    return *supplement;
+}
+
+DEFINE_TRACE(HTMLMediaElementMediaSession)
+{
+    visitor->trace(m_session);
+    WillBeHeapSupplement<HTMLMediaElement>::trace(visitor);
+}
+
+}
+