Reland "Android: Generate JNI code for VideoSink and VideoEncoder"

This is a reland of ba78b5a905bffa05933a135673996df02328f2a4
Original change's description:
> Android: Generate JNI code for VideoSink and VideoEncoder
> 
> This is the first CL to start generating JNI code. It has updated two of
> the most recent classes to use JNI code generation.
> 
> Bug: webrtc:8278
> Change-Id: I1b19ee78c273346ceeaa0401dbdf8696803f16c7
> Reviewed-on: https://webrtc-review.googlesource.com/3820
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#19994}

Bug: webrtc:8278
Change-Id: Id3e6513736eb87d7c234be3b0d13c5d30435201c
Reviewed-on: https://webrtc-review.googlesource.com/4500
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20548}

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

@@ -124,29 +124,35 @@ public interface VideoEncoder {
   /**
    * Initializes the encoding process. Call before any calls to encode.
    */
-  VideoCodecStatus initEncode(Settings settings, Callback encodeCallback);
+  @CalledByNative VideoCodecStatus initEncode(Settings settings, Callback encodeCallback);
+
   /**
    * Releases the encoder. No more calls to encode will be made after this call.
    */
-  VideoCodecStatus release();
+  @CalledByNative VideoCodecStatus release();
+
   /**
    * Requests the encoder to encode a frame.
    */
-  VideoCodecStatus encode(VideoFrame frame, EncodeInfo info);
+  @CalledByNative VideoCodecStatus encode(VideoFrame frame, EncodeInfo info);
+
   /**
    * Informs the encoder of the packet loss and the round-trip time of the network.
    *
    * @param packetLoss How many packets are lost on average per 255 packets.
    * @param roundTripTimeMs Round-trip time of the network in milliseconds.
    */
-  VideoCodecStatus setChannelParameters(short packetLoss, long roundTripTimeMs);
+  @CalledByNative VideoCodecStatus setChannelParameters(short packetLoss, long roundTripTimeMs);
+
   /** Sets the bitrate allocation and the target framerate for the encoder. */
-  VideoCodecStatus setRateAllocation(BitrateAllocation allocation, int framerate);
+  @CalledByNative VideoCodecStatus setRateAllocation(BitrateAllocation allocation, int framerate);
+
   /** Any encoder that wants to use WebRTC provided quality scaler must implement this method. */
-  ScalingSettings getScalingSettings();
+  @CalledByNative ScalingSettings getScalingSettings();
+
   /**
    * Should return a descriptive name for the implementation. Gets called once and cached. May be
    * called from arbitrary thread.
    */
-  String getImplementationName();
+  @CalledByNative String getImplementationName();
 }

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

@@ -19,5 +19,5 @@ public interface VideoSink {
    * this function returns. Each call to retain() should be followed by a call to frame.release()
    * when the reference is no longer needed.
    */
-  void onFrame(VideoFrame frame);
+  @CalledByNative void onFrame(VideoFrame frame);
 }