Add missing headers to new objective-c API.

I missed adding these headers in my inital check-in. This change simply adds
these headers.

Bug: webrtc:9681
Change-Id: Ic2265105cd401d59fac124c2dc1963f0163c5af6
Reviewed-on: https://webrtc-review.googlesource.com/c/103304
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Benjamin Wright <benwright@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24956}

sdk/objc/api/peerconnection/RTCRtpReceiver+Native.h

@@ -11,6 +11,7 @@
 #import "RTCRtpReceiver.h"
 
 #include "api/crypto/framedecryptorinterface.h"
+#include "rtc_base/scoped_ref_ptr.h"
 
 NS_ASSUME_NONNULL_BEGIN
 

sdk/objc/api/peerconnection/RTCRtpSender+Native.h

@@ -11,6 +11,7 @@
 #import "RTCRtpSender.h"
 
 #include "api/crypto/frameencryptorinterface.h"
+#include "rtc_base/scoped_ref_ptr.h"
 
 NS_ASSUME_NONNULL_BEGIN