Decouple MediaSession/MediaSessionObserver from WebContents in Java[OBSOLETE, go to the combined CL]

content/browser/media/session/media_session_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_android.h"
+
+#include <algorithm>
+#include "content/browser/media/session/media_session_impl.h"
+#include "content/browser/web_contents/web_contents_android.h"
+#include "content/common/android/media_metadata_android.h"
+#include "content/public/browser/media_session.h"
+#include "content/public/browser/web_contents.h"
+#include "jni/MediaSessionImpl_jni.h"
+
+namespace content {
+
+using base::android::JavaParamRef;
+
+MediaSessionAndroid::MediaSessionAndroid(MediaSession* session)
+    : MediaSessionObserver(session) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);

[mlamouri (slow - plz ping), 2016/10/28 10:24:50]

Here and below, why do you DCHECK(env)? It's not commonly done.

[Zhiqiang Zhang (Slow), 2016/10/28 11:18:47]

Yes, removed. I saw you used it in AudioFocusDelegate so I thought it was a
common pattern...

+  j_media_session_.Reset(
+      Java_MediaSessionImpl_create(env, reinterpret_cast<intptr_t>(this)));
+}
+
+MediaSessionAndroid::~MediaSessionAndroid() {
+  // MediaSessionDestroyed() should have already been called.
+  DCHECK(j_media_session_.is_null());
+}
+
+// static
+bool MediaSessionAndroid::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+// static
+base::android::ScopedJavaLocalRef<jobject> GetMediaSessionFromWebContents(
+    JNIEnv* env,
+    const JavaParamRef<jclass>& clazz,
+    const JavaParamRef<jobject>& j_contents_android) {
+  WebContents* contents = WebContents::FromJavaWebContents(j_contents_android);
+  DCHECK(contents);

[mlamouri (slow - plz ping), 2016/10/28 10:24:50]

What about early return? Reading WebContents::FromJavaWebContents, `contents`
might be null.

[Zhiqiang Zhang (Slow), 2016/10/28 11:18:48]

Done.

+  MediaSessionImpl* session = MediaSessionImpl::Get(contents);
+  DCHECK(session);
+  return session->session_android()->GetJavaSession();
+}
+
+base::android::ScopedJavaLocalRef<jobject>
+MediaSessionAndroid::GetJavaSession() {
+  return base::android::ScopedJavaLocalRef<jobject>(j_media_session_);
+}
+
+void MediaSessionAndroid::MediaSessionDestroyed() {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  Java_MediaSessionImpl_mediaSessionDestroyed(env, j_media_session_);
+  // Do tear down the Java object since media_session() is going to be nullptr
+  // after this method returns.
+  Java_MediaSessionImpl_tearDown(env, j_media_session_);
+  j_media_session_.Reset();
+}
+
+void MediaSessionAndroid::MediaSessionStateChanged(bool is_controllable,
+                                                   bool is_suspended) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+  Java_MediaSessionImpl_mediaSessionStateChanged(env, j_media_session_,
+                                                 is_controllable, is_suspended);
+}
+
+void MediaSessionAndroid::MediaSessionMetadataChanged(
+    const base::Optional<MediaMetadata>& metadata) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  DCHECK(env);
+
+  // Avoid translating metadata through JNI if there is no Java observer.
+  if (!Java_MediaSessionImpl_hasObservers(env, j_media_session_))
+    return;
+
+  base::android::ScopedJavaLocalRef<jobject> j_metadata;
+  if (metadata.has_value()) {
+    j_metadata = MediaMetadataAndroid::CreateJavaObject(env, metadata.value());
+  }

[mlamouri (slow - plz ping), 2016/10/28 10:24:50]

style: no need for { } 

[Zhiqiang Zhang (Slow), 2016/10/28 11:18:48]

Done.

+  Java_MediaSessionImpl_mediaSessionMetadataChanged(env, j_media_session_,
+                                                    j_metadata);
+}
+
+void MediaSessionAndroid::Resume(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_obj) {
+  DCHECK(media_session());
+  media_session()->Resume(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionAndroid::Suspend(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_obj) {
+  DCHECK(media_session());
+  media_session()->Suspend(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionAndroid::Stop(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_obj) {
+  DCHECK(media_session());
+  media_session()->Stop(MediaSession::SuspendType::UI);
+}
+
+}  // namespace content