Link MediaSessionTabHelper with native MediaSession [CL is going to be split]

content/browser/media/session/media_session_delegate_android.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_delegate_android.h"
+
+#include "base/android/context_utils.h"
+#include "base/android/jni_android.h"
+#include "content/browser/media/session/media_session.h"
+#include "content/common/android/media_metadata_android.h"
+#include "jni/MediaSessionDelegate_jni.h"
+
+using base::android::JavaParamRef;
+
+namespace content {
+
+// static
+bool MediaSessionDelegateAndroid::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+// static
+void MediaSessionDelegateAndroid::CreateAndConnect(
+    MediaSession* session,
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_delegate) {
+  MediaSessionDelegateAndroid* delegate =
+      new MediaSessionDelegateAndroid(session, env, j_delegate);
+  session->PassObserverOwnership(
+      std::unique_ptr<MediaSessionDelegateAndroid>(delegate));
+  Java_MediaSessionDelegate_mediaSessionConnected(
+      env, j_delegate, reinterpret_cast<intptr_t>(delegate));
+}
+
+MediaSessionDelegateAndroid::MediaSessionDelegateAndroid(
+    MediaSession* session,
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_delegate)
+    : MediaSessionObserver(session), j_delegate_(env, j_delegate) {}
+
+MediaSessionDelegateAndroid::~MediaSessionDelegateAndroid() {
+  MediaSessionDisconnected();
+  j_delegate_.reset();

[whywhat, 2016/10/20 22:56:53]

Don't think you need to do this in dtor.

[Zhiqiang Zhang (Slow), 2016/10/21 13:43:52]

Done.

+}
+
+void MediaSessionDelegateAndroid::MediaSessionDisconnected() {
+  MediaSessionObserver::MediaSessionDisconnected();
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  if (!j_delegate_.is_empty()) {

[boliu, 2016/10/21 14:37:15]

this in theory is not safe because gc could run between this check and when you
dereference again in the line below (in practice, dunno what dalvik/art does)

safe way is to dereference first into ScopedJavaLocalRef, then null check the
local ref

[Zhiqiang Zhang (Slow), 2016/10/21 15:05:23]

Done.

+    Java_MediaSessionDelegate_mediaSessionDisconnectedWrapper(
+        env, j_delegate_.get(env));
+  }
+}
+
+void MediaSessionDelegateAndroid::MediaSessionStateChanged(bool is_controllable,
+                                                           bool is_active) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  if (!j_delegate_.is_empty()) {
+    Java_MediaSessionDelegate_mediaSessionStateChanged(
+        env, j_delegate_.get(env), is_controllable, is_active);
+  }
+}
+
+void MediaSessionDelegateAndroid::MediaSessionMetadataChanged(
+    const base::Optional<MediaMetadata>& metadata) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  if (!j_delegate_.is_empty()) {
+    base::android::ScopedJavaLocalRef<jobject> j_metadata;
+    if (metadata.has_value()) {
+      j_metadata =
+          MediaMetadataAndroid::CreateJavaObject(env, metadata.value());
+    }
+    Java_MediaSessionDelegate_mediaSessionMetadataChanged(
+        env, j_delegate_.get(env), j_metadata);
+  }
+}
+
+void MediaSessionDelegateAndroid::ResumeMediaSession(
+    JNIEnv* env,
+    const JavaParamRef<jobject>& obj) {
+  if (session())
+    session()->Resume(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionDelegateAndroid::SuspendMediaSession(
+    JNIEnv* env,
+    const JavaParamRef<jobject>& obj) {
+  if (session())
+    session()->Suspend(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionDelegateAndroid::StopMediaSession(
+    JNIEnv* env,
+    const JavaParamRef<jobject>& obj) {
+  if (session())
+    session()->Stop(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionDelegateAndroid::DisconnectMediaSession(
+    JNIEnv* env,
+    const JavaParamRef<jobject>& obj) {
+  // Will destroy this and send `mediaSessionDisconnected` to Java.
+  if (session())
+    session()->RemoveObserver(this);
+}
+
+}  // namespace content