New class ScopedJavaRefCounted

Intended to be used for holding on to references to the java
EncodedImage and call its release method when no longer used by C++.

Bug: webrtc:9378
Change-Id: I40d917c2bb4217419ef2d609e517566c8466a274
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/154740
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29347}

sdk/android/BUILD.gn

@@ -544,6 +544,7 @@ if (current_os == "linux" || is_android) {
       "src/jni/pc/audio.h",
       "src/jni/pc/logging.cc",
       "src/jni/pc/video.h",
+      "src/jni/scoped_java_ref_counted.h",
     ]
 
     deps = [
@@ -1199,6 +1200,7 @@ if (current_os == "linux" || is_android) {
     sources = [
       "api/org/webrtc/NetworkMonitor.java",
       "api/org/webrtc/NetworkMonitorAutoDetect.java",
+      "api/org/webrtc/RefCounted.java",
       "src/java/org/webrtc/Histogram.java",
       "src/java/org/webrtc/JniCommon.java",
     ]

sdk/android/api/org/webrtc/RefCounted.java

@@ -24,5 +24,5 @@ public interface RefCounted {
    * Decreases ref count by one. When the ref count reaches zero, resources related to the object
    * will be freed.
    */
-  void release();
+  @CalledByNative void release();
 }

sdk/android/src/jni/scoped_java_ref_counted.h

@@ -0,0 +1,54 @@
+/*
+ *  Copyright 2019 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef SDK_ANDROID_SRC_JNI_SCOPED_JAVA_REF_COUNTED_H_
+#define SDK_ANDROID_SRC_JNI_SCOPED_JAVA_REF_COUNTED_H_
+
+#include "sdk/android/native_api/jni/scoped_java_ref.h"
+
+namespace webrtc {
+namespace jni {
+
+// Holds a reference to a java object implementing the RefCounted interface, and
+// calls its release() method from the destructor.
+class ScopedJavaRefCounted {
+ public:
+  // Takes over the caller's reference.
+  static ScopedJavaRefCounted Adopt(JNIEnv* env,
+                                    const JavaRef<jobject>& j_object) {
+    return ScopedJavaRefCounted(env, j_object);
+  }
+
+  ScopedJavaRefCounted(ScopedJavaRefCounted&& other) = default;
+
+  // TODO(nisse): Implement move assignment and copy operations when needed.
+  ScopedJavaRefCounted(const ScopedJavaRefCounted& other) = delete;
+  ScopedJavaRefCounted& operator=(const ScopedJavaRefCounted&) = delete;
+
+  ~ScopedJavaRefCounted() {
+    if (!j_object_.is_null()) {
+      JNIEnv* jni = AttachCurrentThreadIfNeeded();
+      Java_RefCounted_release(jni, j_object_);
+      CHECK_EXCEPTION(jni)
+          << "Unexpected java exception from ScopedJavaRefCounted.release()";
+    }
+  }
+
+ private:
+  // Adopts reference.
+  ScopedJavaRefCounted(JNIEnv* env, const JavaRef<jobject>& j_object)
+      : j_object_(env, j_object) {}
+
+  ScopedJavaGlobalRef<jobject> j_object_;
+};
+
+}  // namespace jni
+}  // namespace webrtc
+
+#endif  // SDK_ANDROID_SRC_JNI_SCOPED_JAVA_REF_COUNTED_H_