Android: Generate Java -> C++ JNI code for VideoEncoder

This is the first CL that tries generating Java -> C++ JNI code.

Bug: webrtc:8278
Change-Id: I1ff0df10db0f80a3c84a61a4e82be8f713690a69
Reviewed-on: https://webrtc-review.googlesource.com/20873
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20592}

sdk/android/src/java/org/webrtc/NativeClassQualifiedName.java

@@ -0,0 +1,31 @@
+/*
+ *  Copyright 2017 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.
+ */
+
+package org.webrtc;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * @NativeClassQualifiedName is used by the JNI generator to create the necessary JNI
+ * bindings to call into the specified native class name.
+ */
+@Target(ElementType.METHOD)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface NativeClassQualifiedName {
+  /*
+   * Tells which native class the method is going to be bound to.
+   * The first parameter of the annotated method must be an int nativePtr pointing to
+   * an instance of this class.
+   */
+  public String value();
+}

sdk/android/src/java/org/webrtc/VideoEncoderWrapper.java

@@ -69,12 +69,13 @@ class VideoEncoderWrapper {
   @CalledByNative
   static VideoEncoder.Callback createEncoderCallback(final long nativeEncoder) {
     return (EncodedImage frame, VideoEncoder.CodecSpecificInfo info)
-               -> onEncodedFrame(nativeEncoder, frame.buffer, frame.encodedWidth,
+               -> nativeOnEncodedFrame(nativeEncoder, frame.buffer, frame.encodedWidth,
                    frame.encodedHeight, frame.captureTimeNs, frame.frameType.getNative(),
                    frame.rotation, frame.completeFrame, frame.qp);
   }
 
-  private static native void onEncodedFrame(long nativeEncoder, ByteBuffer buffer, int encodedWidth,
-      int encodedHeight, long captureTimeNs, int frameType, int rotation, boolean completeFrame,
-      Integer qp);
+  @NativeClassQualifiedName("webrtc::jni::VideoEncoderWrapper")
+  private static native void nativeOnEncodedFrame(long nativeEncoder, ByteBuffer buffer,
+      int encodedWidth, int encodedHeight, long captureTimeNs, int frameType, int rotation,
+      boolean completeFrame, Integer qp);
 }