Update I420Buffer to new VideoFrameBuffer interface

webrtc/sdk/objc/Framework/Classes/Video/objcvideotracksource.mm

 /*
  *  Copyright (c) 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.
  */
 
@@ skipping 35 matching lines @@
     buffer = frame.videoBuffer;
   } else if (frame.nativeHandle) {
     // Adapted CVPixelBuffer frame.
     buffer = new rtc::RefCountedObject<CoreVideoFrameBuffer>(
         static_cast<CVPixelBufferRef>(frame.nativeHandle), adapted_width, adapted_height,
         crop_width, crop_height, crop_x, crop_y);
   } else {
     // Adapted I420 frame.
     // TODO(magjed): Optimize this I420 path.
     rtc::scoped_refptr<I420Buffer> i420_buffer = I420Buffer::Create(adapted_width, adapted_height);
-    i420_buffer->CropAndScaleFrom(*frame.videoBuffer, crop_x, crop_y, crop_width, crop_height);
+    i420_buffer->CropAndScaleFrom(
+        *frame.videoBuffer->ToI420(), crop_x, crop_y, crop_width, crop_height);
     buffer = i420_buffer;
   }
 
   // Applying rotation is only supported for legacy reasons and performance is
   // not critical here.
   webrtc::VideoRotation rotation = static_cast<webrtc::VideoRotation>(frame.rotation);
   if (apply_rotation() && rotation != kVideoRotation_0) {
-    buffer = I420Buffer::Rotate(*buffer->NativeToI420Buffer(), rotation);
+    buffer = I420Buffer::Rotate(*buffer->ToI420(), rotation);
     rotation = kVideoRotation_0;
   }
 
   OnFrame(webrtc::VideoFrame(buffer, rotation, translated_timestamp_us));
 }
 
 }  // namespace webrtc