Compile rtc_api_objc on Mac.

webrtc/api/objc/RTCIceServer.mm

Index: webrtc/api/objc/RTCIceServer.mm
diff --git a/webrtc/api/objc/RTCIceServer.mm b/webrtc/api/objc/RTCIceServer.mm
index 057c69603b0cfb1f5e9c559bb9467c8bec1c7fe2..bdac700e554d14f7647ed719070180428a2850c3 100644
--- a/webrtc/api/objc/RTCIceServer.mm
+++ b/webrtc/api/objc/RTCIceServer.mm
@@ -14,19 +14,22 @@
 #import "webrtc/base/objc/NSString+StdString.h"
 
 @implementation RTCIceServer
+// TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
 
 @synthesize urlStrings = _urlStrings;
 @synthesize username = _username;
 @synthesize credential = _credential;
 
-- (instancetype)initWithURLStrings:(NSArray<NSString *> *)urlStrings {
+- (instancetype)initWithURLStrings:(NSArray *)urlStrings {
+// - (instancetype)initWithURLStrings:(NSArray<NSString *> *)urlStrings {
   NSParameterAssert(urlStrings.count);
   return [self initWithURLStrings:urlStrings
                          username:nil
                        credential:nil];
 }
 
-- (instancetype)initWithURLStrings:(NSArray<NSString *> *)urlStrings
+- (instancetype)initWithURLStrings:(NSArray *)urlStrings
+// - (instancetype)initWithURLStrings:(NSArray<NSString *> *)urlStrings
                           username:(NSString *)username
                         credential:(NSString *)credential {
   NSParameterAssert(urlStrings.count);