Refactor some ObjC API init methods.

webrtc/api/objc/RTCPeerConnection+Private.h

Index: webrtc/api/objc/RTCPeerConnection+Private.h
diff --git a/webrtc/api/objc/RTCPeerConnection+Private.h b/webrtc/api/objc/RTCPeerConnection+Private.h
index feac8be6d96a3c485c955d2506766fa1c7baf57d..031631a37a9dbc1772a4f20cca466e8be81e5f82 100644
--- a/webrtc/api/objc/RTCPeerConnection+Private.h
+++ b/webrtc/api/objc/RTCPeerConnection+Private.h
@@ -58,6 +58,19 @@ class PeerConnectionDelegateAdapter : public PeerConnectionObserver {
 @property(nonatomic, readonly)
     rtc::scoped_refptr<webrtc::PeerConnectionInterface> nativePeerConnection;
 
+/** Initialize an RTCPeerConnection with a configuration, constraints, and
+ *  delegate.
+ */
+- (instancetype)initWithFactory:
+    (RTCPeerConnectionFactory *)factory
+                  configuration:
+    (RTCConfiguration *)configuration
+                    constraints:
+    (RTCMediaConstraints *)constraints
+                       delegate:
+    (nullable id<RTCPeerConnectionDelegate>)delegate
+    NS_DESIGNATED_INITIALIZER;
+
 + (webrtc::PeerConnectionInterface::SignalingState)nativeSignalingStateForState:
     (RTCSignalingState)state;