Decouple MediaSession messages from WebContents (full patch)

content/browser/media/session/media_session_android.h

Index: content/browser/media/session/media_session_android.h
diff --git a/content/browser/media/session/media_session_android.h b/content/browser/media/session/media_session_android.h
new file mode 100644
index 0000000000000000000000000000000000000000..fb3644070faa44a7d9e19ad1e5e2fe69ce4d1bb5
--- /dev/null
+++ b/content/browser/media/session/media_session_android.h
@@ -0,0 +1,62 @@
+// 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.
+
+#ifndef CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_ANDROID_H_
+#define CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_ANDROID_H_
+
+#include <jni.h>
+#include <memory>
+#include <vector>
+
+#include "base/android/jni_weak_ref.h"
+#include "base/android/scoped_java_ref.h"
+#include "content/public/browser/media_session_observer.h"
+
+namespace content {
+
+class MediaSessionImpl;
+class WebContentsAndroid;
+
+// This class is interlayer between native MediaSession and Java
+// MediaSession. This class is owned by the native MediaSession and will
+// teardown Java MediaSession when the native MediaSession is destroyed.
+// Java MediaSessionObservers are also proxied via this class.
+class MediaSessionAndroid final : public MediaSessionObserver {
+ public:
+  // Helper class for calling GetJavaObject() in a static method, in order to
+  // avoid leaking the Java object outside.
+  struct JavaObjectGetter;
+
+  static bool Register(JNIEnv* env);
+
+  explicit MediaSessionAndroid(MediaSessionImpl* session);
+  ~MediaSessionAndroid() override;
+
+  // MediaSessionObserver implementation.
+  void MediaSessionDestroyed() override;
+  void MediaSessionStateChanged(bool is_controllable,
+                                bool is_suspended) override;
+  void MediaSessionMetadataChanged(
+      const base::Optional<MediaMetadata>& metadata) override;
+
+  // MediaSession method wrappers.
+  void Resume(JNIEnv* env, const base::android::JavaParamRef<jobject>& j_obj);
+  void Suspend(JNIEnv* env, const base::android::JavaParamRef<jobject>& j_obj);
+  void Stop(JNIEnv* env, const base::android::JavaParamRef<jobject>& j_obj);
+
+ private:
+  WebContentsAndroid* GetWebContentsAndroid();
+
+  base::android::ScopedJavaLocalRef<jobject> GetJavaObject();
+
+  // The linked Java object. The strong reference is hold by Java WebContensImpl
+  // to avoid introducing a new GC root.
+  JavaObjectWeakGlobalRef j_media_session_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSessionAndroid);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_ANDROID_H_