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/android/media_session.h"
+#include "content/common/frame_messages.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) {}
+
+// Clients must call this after construction and destroy the controller if it
+// returns false.
+bool MediaSessionController::Initialize(bool has_audio,
+                                        bool is_remote,
+                                        base::TimeDelta duration) {
+  // These objects are only created on the UI thread, so this is safe.

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

`DCHECK_CURRENTLY_ON(BrowserThread::UI);` or it's a lie :)

[DaleCurtis, 2016/01/23 02:10:59]

Done.

+  static uint32_t player_id = 0;
+  player_id_ = static_cast<int>(player_id++);
+  has_audio_ = has_audio;
+
+  // Don't bother with a MediaSession for remote players or without audio.
+  if (!has_audio || is_remote)
+    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.
+  if (!MediaSession::Get(media_web_contents_observer_->web_contents())
+           ->AddPlayer(this, player_id_, media_session_type)) {
+    OnSuspend(player_id_);
+    return false;
+  }
+
+  initialized_ = true;
+  return true;
+}
+
+MediaSessionController::~MediaSessionController() {

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

style: keep implementations in the same order as the declarations.

[DaleCurtis, 2016/01/23 02:10:59]

Done.

+  if (initialized_) {

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

nit:
```
if (!initialized_)
  return;
// do stuff
```

[DaleCurtis, 2016/01/23 02:10:59]

Done.

+    MediaSession::Get(media_web_contents_observer_->web_contents())
+        ->RemovePlayer(this, player_id_);
+  }
+}
+
+void MediaSessionController::OnSuspend(int player_id) {
+  DCHECK_EQ(player_id_, player_id);
+  media_web_contents_observer_->Send(
+      new FrameMsg_MediaDelegatePause(id_.first->GetRoutingID(), id_.second));
+}
+
+void MediaSessionController::OnResume(int player_id) {
+  DCHECK_EQ(player_id_, player_id);
+  media_web_contents_observer_->Send(
+      new FrameMsg_MediaDelegatePlay(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 FrameMsg_MediaDelegateVolumeMultiplierUpdate(
+          id_.first->GetRoutingID(), id_.second, volume_multiplier));
+}
+
+void MediaSessionController::PausePlayback() {
+  MediaSession* session =
+      MediaSession::Get(media_web_contents_observer_->web_contents());
+  // 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 (!session->IsSuspended())
+    session->OnPlayerPaused(this, player_id_);
+}
+
+}  // namespace content