Added DtlsCertificate, a ref counted object owning an SSLIdentity

talk/app/webrtc/objc/RTCPeerConnection.mm

Index: talk/app/webrtc/objc/RTCPeerConnection.mm
diff --git a/talk/app/webrtc/objc/RTCPeerConnection.mm b/talk/app/webrtc/objc/RTCPeerConnection.mm
index 0d30acc0eb23ba6b00c8ea16eacfba8cf7d78fbc..9823a6bf8130413d3ccf3e28a873d6a399258bc8 100644
--- a/talk/app/webrtc/objc/RTCPeerConnection.mm
+++ b/talk/app/webrtc/objc/RTCPeerConnection.mm
@@ -275,11 +275,15 @@ class RTCStatsObserver : public StatsObserver {
 - (instancetype)initWithFactory:(webrtc::PeerConnectionFactoryInterface*)factory
      iceServers:(const webrtc::PeerConnectionInterface::IceServers&)iceServers
     constraints:(const webrtc::MediaConstraintsInterface*)constraints {
-  NSParameterAssert(factory != NULL);
+  NSParameterAssert(factory != nullptr);
   if (self = [super init]) {
     _observer.reset(new webrtc::RTCPeerConnectionObserver(self));
     _peerConnection = factory->CreatePeerConnection(
-        iceServers, constraints, NULL, NULL, _observer.get());
+        iceServers,
+        constraints,
+        nullptr,
+        rtc::scoped_ptr<webrtc::DtlsIdentityStoreInterface>(nullptr).Pass(),
+        _observer.get());
     _localStreams = [[NSMutableArray alloc] init];
   }
   return self;
@@ -293,7 +297,12 @@ class RTCStatsObserver : public StatsObserver {
   if (self = [super init]) {
     _observer.reset(new webrtc::RTCPeerConnectionObserver(self));
     _peerConnection =
-        factory->CreatePeerConnection(config, constraints, nullptr, nullptr, _observer.get());
+        factory->CreatePeerConnection(
+            config,
+            constraints,
+            nullptr,
+            rtc::scoped_ptr<webrtc::DtlsIdentityStoreInterface>(nullptr).Pass(),
+            _observer.get());
     _localStreams = [[NSMutableArray alloc] init];
     _delegate = delegate;
   }