Compile rtc_api_objc on Mac.

webrtc/api/objc/RTCConfiguration.h

Index: webrtc/api/objc/RTCConfiguration.h
diff --git a/webrtc/api/objc/RTCConfiguration.h b/webrtc/api/objc/RTCConfiguration.h
index 144c8d3bd5ebe041b2309809d684e73db7abf5c3..ed4bfc27487aa64b06a3d205270f5ac9ab2488fe 100644
--- a/webrtc/api/objc/RTCConfiguration.h
+++ b/webrtc/api/objc/RTCConfiguration.h
@@ -12,6 +12,8 @@
 
 @class RTCIceServer;
 
+// TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
+
 /**
  * Represents the ice transport policy. This exposes the same states in C++,
  * which include one more state than what exists in the W3C spec.
@@ -53,7 +55,8 @@ NS_ASSUME_NONNULL_BEGIN
 @interface RTCConfiguration : NSObject
 
 /** An array of Ice Servers available to be used by ICE. */
-@property(nonatomic, copy) NSArray<RTCIceServer *> *iceServers;
+@property(nonatomic, copy, nonnull) NSArray *iceServers;
+// @property(nonatomic, copy) NSArray<RTCIceServer *> *iceServers;
 
 /** Which candidates the ICE agent is allowed to use. The W3C calls it
  * |iceTransportPolicy|, while in C++ it is called |type|. */
@@ -72,7 +75,7 @@ NS_ASSUME_NONNULL_BEGIN
 /** Key type used to generate SSL identity. Default is ECDSA. */
 @property(nonatomic, assign) RTCEncryptionKeyType keyType;
 
-- (instancetype)init NS_DESIGNATED_INITIALIZER;
+- (nonnull instancetype)init NS_DESIGNATED_INITIALIZER;
 
 @end