Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/session/media_session_controllers_manager.cc

+// 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 "content/browser/media/session/media_session_controllers_manager.h"
+
+#include "base/command_line.h"
+#include "content/browser/media/session/media_session.h"
+#include "content/browser/media/session/media_session_controller.h"
+#include "content/browser/media/session/media_session_observer.h"
+#include "media/base/media_switches.h"
+
+namespace content {
+
+namespace {
+
+bool IsDefaultMediaSessionEnabled() {
+#if defined(OS_ANDROID)
+  return true;
+#else
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableDefaultMediaSession);
+#endif
+}
+
+}  // anonymous namespace
+
+MediaSessionControllersManager::MediaSessionControllersManager(
+    MediaWebContentsObserver* media_web_contents_observer)
+    : media_web_contents_observer_(media_web_contents_observer) {
+}
+
+MediaSessionControllersManager::~MediaSessionControllersManager() = default;
+
+void MediaSessionControllersManager::Clear(RenderFrameHost* render_frame_host) {
+  if (!IsDefaultMediaSessionEnabled())
+    return;
+
+  for (auto it = controllers_map_.begin(); it != controllers_map_.end();) {
+    if (it->first.first == render_frame_host)
+      it = controllers_map_.erase(it);
+    else
+      ++it;
+  }
+}
+
+bool MediaSessionControllersManager::RequestPlay(const MediaPlayerId& id,
+    bool has_audio, bool is_remote, base::TimeDelta duration) {
+  if (!IsDefaultMediaSessionEnabled())
+    return true;
+
+  // Since we don't remove session instances on pause, there may be an existing
+  // instance for this playback attempt.
+  //
+  // In this case, try to reinitialize it with the new settings.  If they are
+  // the same, this is a no-op.  If the reinitialize fails, destroy the
+  // controller. A later playback attempt will create a new controller.
+  auto it = controllers_map_.find(id);
+  if (it != controllers_map_.end()) {
+    if (!it->second->Initialize(has_audio, is_remote, duration))
+      controllers_map_.erase(it);
+    return false;
+  }
+
+  scoped_ptr<MediaSessionController> controller(
+      new MediaSessionController(id, media_web_contents_observer_));
+
+  if (!controller->Initialize(has_audio, is_remote, duration))
+    return false;
+
+  controllers_map_[id] = std::move(controller);
+  return true;
+}
+
+void MediaSessionControllersManager::OnPause(const MediaPlayerId& id) {
+  if (!IsDefaultMediaSessionEnabled())
+    return;
+
+  auto it = controllers_map_.find(id);
+  if (it == controllers_map_.end())
+    return;
+
+  it->second->OnPlaybackPaused();
+}
+
+void MediaSessionControllersManager::OnEnd(const MediaPlayerId& id) {
+  if (!IsDefaultMediaSessionEnabled())
+    return;
+  controllers_map_.erase(id);
+}
+
+}  // namespace content