Android: Generate JNI code for androidvideotracksource

Bug: webrtc:8278
Change-Id: I43b53c68ebaf2c3f9c27ea7ef510d7b016c1df93
Reviewed-on: https://webrtc-review.googlesource.com/23243
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20795}

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

@@ -51,6 +51,7 @@ public class VideoFrame {
      * Crops a region defined by |cropx|, |cropY|, |cropWidth| and |cropHeight|. Scales it to size
      * |scaleWidth| x |scaleHeight|.
      */
+    @CalledByNative("Buffer")
     Buffer cropAndScale(
         int cropX, int cropY, int cropWidth, int cropHeight, int scaleWidth, int scaleHeight);
   }