Move audio focus control from media/ to content/ and make it per WebContents.

content/browser/media/android/media_session.cc

+// Copyright 2015 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.h"
+
+#include "base/android/jni_android.h"
+#include "content/browser/media/android/media_session_observer.h"
+#include "jni/MediaSession_jni.h"
+
+namespace content {
+
+DEFINE_WEB_CONTENTS_USER_DATA_KEY(MediaSession);
+
+// static
+bool content::MediaSession::RegisterMediaSession(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+// static
+MediaSession* MediaSession::Get(WebContents* web_contents) {
+  MediaSession* session = FromWebContents(web_contents);
+  if (!session) {
+    CreateForWebContents(web_contents);
+    session = FromWebContents(web_contents);
+    session->Initialize();
+  }
+  return session;
+}
+
+MediaSession::PlayerIdentifier::PlayerIdentifier(MediaSessionObserver* observer,
+                                                 int player_id)
+    : observer(observer),
+      player_id(player_id) {
+}
+
+bool MediaSession::PlayerIdentifier::operator==(
+    const PlayerIdentifier& other) const {
+  return this->observer == other.observer && this->player_id == other.player_id;
+}
+
+size_t MediaSession::PlayerIdentifier::Hash::operator()(
+    const PlayerIdentifier& player_identifier) const {
+  size_t hash = BASE_HASH_NAMESPACE::hash<MediaSessionObserver*>()(
+      player_identifier.observer);
+  hash += BASE_HASH_NAMESPACE::hash<int>()(player_identifier.player_id);
+  return hash;
+}
+
+MediaSession::~MediaSession() {
+  DCHECK(players_.empty());
+  DCHECK(!has_audio_focus_);
+}
+
+void MediaSession::Initialize() {

[Ted C, 2015/05/27 00:59:08]

the ordering of methods should match the header

[mlamouri (slow - plz ping), 2015/05/28 16:20:40]

Done.

+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  j_media_session_.Reset(Java_MediaSession_createMediaSession(
+      env,
+      base::android::GetApplicationContext(),
+      reinterpret_cast<intptr_t>(this)));
+}
+
+MediaSession::MediaSession(WebContents* web_contents)
+    : WebContentsObserver(web_contents),
+      has_audio_focus_(false),
+      audio_focus_type_(Type::Transient) {
+}
+
+bool MediaSession::AddPlayer(MediaSessionObserver* observer,
+                             int player_id,
+                             Type type) {
+  // If the audio focus is already granted and is of type Content, there is
+  // nothing to do. If it is granted of type Transient the requested type is
+  // also transient, there is also nothing to do. Otherwise, the session needs
+  // to request audio focus again.
+  if (has_audio_focus_ &&
+      (audio_focus_type_ == Type::Content || audio_focus_type_ == type)) {
+    players_.insert(PlayerIdentifier(observer, player_id));
+    return true;
+  }
+
+  bool had_audio_focus = has_audio_focus_;
+  has_audio_focus_ = RequestSystemAudioFocus(type);
+  audio_focus_type_ = type;
+
+  if (!has_audio_focus_)
+    return false;
+
+  // The session should be reset if a player is starting while all players are
+  // suspended.
+  if (!had_audio_focus)
+    players_.clear();
+
+  players_.insert(PlayerIdentifier(observer, player_id));
+
+  return true;
+}
+
+void MediaSession::RemovePlayer(MediaSessionObserver* observer,
+                                int player_id) {
+  auto it = players_.find(PlayerIdentifier(observer, player_id));
+  if (it != players_.end())
+    players_.erase(it);
+
+  AbandonSystemAudioFocusIfNeeded();
+}
+
+void MediaSession::RemovePlayers(MediaSessionObserver* observer) {
+  for (auto it = players_.begin(); it != players_.end(); ) {

[Ted C, 2015/05/27 00:59:08]

extra space after the last ;

[mlamouri (slow - plz ping), 2015/05/28 16:20:39]

Done.

[Ted C, 2015/05/28 20:46:45]

I meant that you didn't need the extra space, now there are two :-)

[mlamouri (slow - plz ping), 2015/05/29 11:14:13]

OK. Fixed :)

+    if (it->observer == observer)
+      players_.erase(it++);
+    else
+      ++it;
+  }
+
+  AbandonSystemAudioFocusIfNeeded();
+}
+
+bool MediaSession::RequestSystemAudioFocus(Type type) {
+  if (j_media_session_.is_null())

[Ted C, 2015/05/27 00:59:08]

how could this be null?  initialize is called after being constructed and the
object only goes away when this class dies.

[mlamouri (slow - plz ping), 2015/05/28 16:20:39]

It is reset by content_browsertests to cut down the Android bits. I agree that
it's not ideal but that's the best way I found to be able to test this class
without being affected by Android API side effects.

+    return true;
+
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  return Java_MediaSession_requestAudioFocus(env, j_media_session_.obj(),
+                                             type == Type::Transient);
+}
+
+void MediaSession::AbandonSystemAudioFocusIfNeeded() {
+  if (!has_audio_focus_ || !players_.empty())

[Ted C, 2015/05/27 00:59:08]

what happens if we had previously got a OnSuspend from java (like the
AUDIOFOCUS_LOSS_TRANSIENT case) and in the mean time we remove all the players. 
In that case, we never call abandonAudioFocus.

Does it happen through some other means?

[mlamouri (slow - plz ping), 2015/05/28 16:20:40]

Good catch. Should be fixed.

+    return;
+
+  if (!j_media_session_.is_null()) {
+    JNIEnv* env = base::android::AttachCurrentThread();
+    DCHECK(env);
+    Java_MediaSession_abandonAudioFocus(env, j_media_session_.obj());
+  }
+
+  has_audio_focus_ = false;
+}
+
+void MediaSession::OnSuspend(JNIEnv* env, jobject obj) {
+  OnSuspend();
+}
+
+void MediaSession::OnSuspend() {
+  has_audio_focus_ = false;
+
+  for (const auto& it : players_)
+    it.observer->OnSuspend(it.player_id);
+}
+

[Ted C, 2015/05/27 00:59:08]

unnecessary extra blank line 

[mlamouri (slow - plz ping), 2015/05/28 16:20:40]

Done.

[mlamouri (slow - plz ping), 2015/05/28 16:20:40]

Done.

+
+void MediaSession::OnResume(JNIEnv* env, jobject obj) {
+  OnResume();
+}
+
+void MediaSession::OnResume() {
+  has_audio_focus_ = true;
+
+  for (const auto& it : players_)
+    it.observer->OnResume(it.player_id);
+}
+
+void MediaSession::ResetJavaRefForTest() {
+  j_media_session_.Reset();
+}
+
+MediaSession::Type MediaSession::audio_focus_type_for_test() const {
+  return audio_focus_type_;
+}
+
+bool MediaSession::has_audio_focus_for_test() const {
+  return has_audio_focus_;
+}
+
+}  // namespace content