Compile rtc_api_objc on Mac.

webrtc/api/objc/RTCPeerConnection+Stats.mm

Index: webrtc/api/objc/RTCPeerConnection+Stats.mm
diff --git a/webrtc/api/objc/RTCPeerConnection+Stats.mm b/webrtc/api/objc/RTCPeerConnection+Stats.mm
index 5032c84e54b6497ff43cc4900707012aaa1d72f8..028909dcbbe8c1c7193a35e56b9e4db5be4472f4 100644
--- a/webrtc/api/objc/RTCPeerConnection+Stats.mm
+++ b/webrtc/api/objc/RTCPeerConnection+Stats.mm
@@ -21,7 +21,7 @@ namespace webrtc {
 class StatsObserverAdapter : public StatsObserver {
  public:
   StatsObserverAdapter(void (^completionHandler)
-      (NSArray<RTCStatsReport *> *stats)) {
+      (NSArray/*<RTCStatsReport *>*/ *stats)) {
     completion_handler_ = completionHandler;
   }
 
@@ -42,7 +42,7 @@ class StatsObserverAdapter : public StatsObserver {
   }
 
  private:
-  void (^completion_handler_)(NSArray<RTCStatsReport *> *stats);
+  void (^completion_handler_)(NSArray/*<RTCStatsReport *>*/ *stats);
 };
 }  // namespace webrtc
 
@@ -51,7 +51,7 @@ class StatsObserverAdapter : public StatsObserver {
 - (void)statsForTrack:(RTCMediaStreamTrack *)mediaStreamTrack
      statsOutputLevel:(RTCStatsOutputLevel)statsOutputLevel
     completionHandler:
-    (void (^)(NSArray<RTCStatsReport *> *stats))completionHandler {
+    (void (^)(NSArray/*<RTCStatsReport *>*/ *stats))completionHandler {
   rtc::scoped_refptr<webrtc::StatsObserverAdapter> observer(
       new rtc::RefCountedObject<webrtc::StatsObserverAdapter>
           (completionHandler));