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)
+{
+    if (HTMLMediaElementMediaSession* supplement = fromIfExists(mediaElement))
+        return supplement->m_session.get();
+    return nullptr;
+}
+
+void HTMLMediaElementMediaSession::setSession(HTMLMediaElement& mediaElement, MediaSession* session)
+{
+    from(mediaElement).m_session = session;
+}
+
+const char* HTMLMediaElementMediaSession::supplementName()
+{
+    return "HTMLMediaElementMediaSession";
+}
+
+HTMLMediaElementMediaSession& HTMLMediaElementMediaSession::from(HTMLMediaElement& element)
+{
+    HTMLMediaElementMediaSession* supplement = fromIfExists(element);
+    if (!supplement) {
+        supplement = new HTMLMediaElementMediaSession();
+        provideTo(element, supplementName(), adoptPtrWillBeNoop(supplement));
+    }
+    return *supplement;
+}
+
+HTMLMediaElementMediaSession* HTMLMediaElementMediaSession::fromIfExists(HTMLMediaElement& element)
+{
+    return static_cast<HTMLMediaElementMediaSession*>(WillBeHeapSupplement<HTMLMediaElement>::from(element, supplementName()));
+}
+
+DEFINE_TRACE(HTMLMediaElementMediaSession)
+{
+    visitor->trace(m_session);
+    WillBeHeapSupplement<HTMLMediaElement>::trace(visitor);
+}
+
+}
+