Add the URL attribute to cricket::Candiate. (Objc wrapper)

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIceCandidate.h

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIceCandidate.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIceCandidate.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIceCandidate.h
index 9f472b8df057a432b389c1122a1368524c8200c1..e381045748792dd2c27eb2b7d27d8d4a55dab2ab 100644
--- a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIceCandidate.h
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIceCandidate.h
@@ -32,6 +32,9 @@ RTC_EXPORT
 /** The SDP string for this candidate. */
 @property(nonatomic, readonly) NSString *sdp;
 
+/** The URL of the ICE server which this candidate is gathered from. */
+@property(nonatomic, readonly) NSString *serverUrl;
+
 - (instancetype)init NS_UNAVAILABLE;
 
 /**
@@ -40,6 +43,7 @@ RTC_EXPORT
 - (instancetype)initWithSdp:(NSString *)sdp
               sdpMLineIndex:(int)sdpMLineIndex
                      sdpMid:(nullable NSString *)sdpMid
+                  serverUrl:(nullable NSString *)serverUrl

[tkchin_webrtc, 2017/02/13 23:29:50]

This is a breaking API change. Can we keep the old ctor and mark it deprecated?
And have the old one call into this new designated one?

[Taylor Brandstetter, 2017/02/13 23:53:00]

Also, since the URL is only something that comes out of the PeerConnection, not
into it, the constructor that takes a URL should be private.

[Zhi Huang, 2017/02/14 19:09:08]

Oh, you are right. We should keep both constructors for now.

Taylor:
If we make the constructor with "url" private, that means we won't deprecate the
other one, right? Because the constructor would be called in other places like
(https://cs.corp.google.com/piper///depot/google3/third_party/objective_c/Tach...)
and we need at least one public constructor.

[Taylor Brandstetter, 2017/02/14 21:40:03]

Right. An application shouldn't ever need to construct a candidate with a URL,
so the existing constructor is good.

     NS_DESIGNATED_INITIALIZER;
 
 @end