Make MediaSession per frame as an attribute of Navigator

third_party/WebKit/Source/modules/mediasession/NavigatorMediaSession.cpp

+// Copyright 2016 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 "modules/mediasession/NavigatorMediaSession.h"
+
+#include "bindings/core/v8/ExceptionStatePlaceholder.h"
+#include "modules/mediasession/MediaSession.h"
+#include "platform/Supplementable.h"
+
+namespace blink {
+
+NavigatorMediaSession::NavigatorMediaSession(Navigator&) {}
+
+DEFINE_TRACE(NavigatorMediaSession) {
+  visitor->trace(m_session);
+  Supplement<Navigator>::trace(visitor);
+}
+
+const char* NavigatorMediaSession::supplementName() {
+  return "NavigatorMediaSession";
+}
+
+NavigatorMediaSession& NavigatorMediaSession::from(Navigator& navigator) {
+  NavigatorMediaSession* supplement = static_cast<NavigatorMediaSession*>(
+      Supplement<Navigator>::from(navigator, supplementName()));
+  if (!supplement) {
+    supplement = new NavigatorMediaSession(navigator);
+    provideTo(navigator, supplementName(), supplement);
+  }
+  return *supplement;
+}
+
+MediaSession* NavigatorMediaSession::mediaSession(Navigator& navigator) {
+  NavigatorMediaSession& self = NavigatorMediaSession::from(navigator);
+  if (!self.m_session)
+    self.m_session = MediaSession::create();
+  return self.m_session.get();
+}
+
+}  // namespace blink