Create experimental Obj-C++ API.

This can be used to wrap Objective-C components in C++ classes, so users
can use the WebRTC C++ API directly together with the iOS specific
components provided by our SDK.

Bug: webrtc:8832
Change-Id: I6d34f7ec62d51df8d3a5340a2e17d30ae73e13e8
Reviewed-on: https://webrtc-review.googlesource.com/46162
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21850}

sdk/objc/Framework/Classes/PeerConnection/RTCVideoFrame.mm

@@ -15,6 +15,8 @@
 
 #include "api/video/video_frame.h"
 #include "rtc_base/timeutils.h"
+#include "sdk/objc/Framework/Native/api/video_frame_buffer.h"
+#include "sdk/objc/Framework/Native/src/objc_frame_buffer.h"
 
 id<RTCVideoFrameBuffer> nativeToRtcFrameBuffer(
     const rtc::scoped_refptr<webrtc::VideoFrameBuffer> &buffer) {
@@ -104,7 +106,7 @@ id<RTCVideoFrameBuffer> nativeToRtcFrameBuffer(
 
 - (webrtc::VideoFrame)nativeVideoFrame {
   rtc::scoped_refptr<webrtc::VideoFrameBuffer> frameBuffer =
-      new rtc::RefCountedObject<webrtc::ObjCFrameBuffer>(self.buffer);
+      webrtc::ObjCToNativeVideoFrameBuffer(self.buffer);
   webrtc::VideoFrame videoFrame(frameBuffer,
                                 (webrtc::VideoRotation)self.rotation,
                                 self.timeStampNs / rtc::kNumNanosecsPerMicrosec);