Implement MediaSession on top of the WebMediaPlayerDelegate.

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/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++);
+  }
+
+  // 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 we were previously initialized and a different session type has been
+  // requested, release the existing session.
+  if (has_session_ && media_session_type != session_type_) {
+    has_session_ = false;
+    media_session_->RemovePlayer(this, player_id_);
+  }
+
+  // If a session can't be created, force a pause immediately.
+  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