RTC_OBJC_TYPE RTCWrappedNativeVideo{Decoder,Encoder}.

Some versionss of WebKit.framework export these symbols. Even if they
are private symbols, WebRTC needs to provide a way to prefix them like
the OBJC API symbols (see [1]).

[1] - https://webrtc-review.googlesource.com/c/src/+/173781

Bug: None
Change-Id: Ibb9ca2c89796a0d5e2ca65c549ba8799f24bbe7c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/182421
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31987}

sdk/objc/api/video_codec/RTCVideoEncoderVP9.mm

@@ -11,6 +11,7 @@
 
 #import <Foundation/Foundation.h>
 
+#import "RTCMacros.h"
 #import "RTCVideoEncoderVP9.h"
 #import "RTCWrappedNativeVideoEncoder.h"
 
@@ -19,7 +20,7 @@
 @implementation RTC_OBJC_TYPE (RTCVideoEncoderVP9)
 
 + (id<RTC_OBJC_TYPE(RTCVideoEncoder)>)vp9Encoder {
-  return [[RTCWrappedNativeVideoEncoder alloc]
+  return [[RTC_OBJC_TYPE(RTCWrappedNativeVideoEncoder) alloc]
       initWithNativeEncoder:std::unique_ptr<webrtc::VideoEncoder>(webrtc::VP9Encoder::Create())];
 }