Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/android/media_session_controller.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/android/media_session_controller.h"
-
-#include "content/browser/media/android/media_session.h"
-#include "content/browser/media/media_web_contents_observer.h"
-#include "content/common/media/media_player_delegate_messages.h"
-#include "content/public/browser/browser_thread.h"
-#include "content/public/browser/render_frame_host.h"
-
-namespace content {
-
-MediaSessionController::MediaSessionController(
-    const WebContentsObserver::MediaPlayerId& id,
-    MediaWebContentsObserver* media_web_contents_observer)
-    : id_(id),
-      media_web_contents_observer_(media_web_contents_observer),
-      media_session_(
-          MediaSession::Get(media_web_contents_observer_->web_contents())) {}
-
-MediaSessionController::~MediaSessionController() {
-  if (!has_session_)
-    return;
-  media_session_->RemovePlayer(this, player_id_);
-}
-
-bool MediaSessionController::Initialize(bool has_audio,
-                                        bool is_remote,
-                                        base::TimeDelta duration) {
-  // Don't generate a new id if one has already been set.
-  if (!has_session_) {
-    // These objects are only created on the UI thread, so this is safe.
-    DCHECK_CURRENTLY_ON(BrowserThread::UI);
-    static uint32_t player_id = 0;
-    player_id_ = static_cast<int>(player_id++);
-  } else {
-    // WebMediaPlayerAndroid does not have an accurate sense of audio presence,
-    // only the MediaPlayerManager does, so WMPA never reports audio unless it's
-    // sure (no video stream).  This leads to issues when Initialize() is called
-    // by WMPA (reporting no audio and subsequently releasing the session) after
-    // the manager accurately reported audio.
-    //
-    // To workaround this, |has_audio| is sticky; I.e., once a session has been
-    // created with audio all future sessions will also have audio.
-    //
-    // TODO(dalecurtis): Delete sticky audio once we're no longer using WMPA and
-    // the BrowserMediaPlayerManagers.  Tracked by http://crbug.com/580626
-    has_audio = true;
-  }
-
-  // Don't bother with a MediaSession for remote players or without audio.  If
-  // we already have a session from a previous call, release it.
-  if (!has_audio || is_remote) {
-    if (has_session_) {
-      has_session_ = false;
-      media_session_->RemovePlayer(this, player_id_);
-    }
-    return true;
-  }
-
-  const MediaSession::Type media_session_type =
-      duration == base::TimeDelta() ||
-              duration >
-                  base::TimeDelta::FromSeconds(kMinimumDurationForContentSecs)
-          ? MediaSession::Type::Content
-          : MediaSession::Type::Transient;
-
-  // If a session can't be created, force a pause immediately.  Attempt to add a
-  // session even if we already have one.  MediaSession expects AddPlayer() to
-  // be called after OnPlaybackPaused() to reactivate the session.
-  if (!media_session_->AddPlayer(this, player_id_, media_session_type)) {
-    OnSuspend(player_id_);
-    return false;
-  }
-
-  has_session_ = true;
-  return true;
-}
-
-void MediaSessionController::OnSuspend(int player_id) {
-  DCHECK_EQ(player_id_, player_id);
-  media_web_contents_observer_->Send(
-      new MediaPlayerDelegateMsg_Pause(id_.first->GetRoutingID(), id_.second));
-}
-
-void MediaSessionController::OnResume(int player_id) {
-  DCHECK_EQ(player_id_, player_id);
-  media_web_contents_observer_->Send(
-      new MediaPlayerDelegateMsg_Play(id_.first->GetRoutingID(), id_.second));
-}
-
-void MediaSessionController::OnSetVolumeMultiplier(int player_id,
-                                                   double volume_multiplier) {
-  DCHECK_EQ(player_id_, player_id);
-  media_web_contents_observer_->Send(
-      new MediaPlayerDelegateMsg_UpdateVolumeMultiplier(
-          id_.first->GetRoutingID(), id_.second, volume_multiplier));
-}
-
-void MediaSessionController::OnPlaybackPaused() {
-  // We check for suspension here since the renderer may issue its own pause
-  // in response to or while a pause from the browser is in flight.
-  if (!media_session_->IsSuspended())
-    media_session_->OnPlayerPaused(this, player_id_);
-}
-
-}  // namespace content