Update iOS AppRTCDemo to use the updated Objective-C API.

webrtc/examples/objc/AppRTCDemo/RTCSessionDescription+JSON.m

 /*
  *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #import "RTCSessionDescription+JSON.h"
 
 static NSString const *kRTCSessionDescriptionTypeKey = @"type";
 static NSString const *kRTCSessionDescriptionSdpKey = @"sdp";
 
 @implementation RTCSessionDescription (JSON)
 
 + (RTCSessionDescription *)descriptionFromJSONDictionary:
     (NSDictionary *)dictionary {
-  NSString *type = dictionary[kRTCSessionDescriptionTypeKey];
+  NSString *typeString = dictionary[kRTCSessionDescriptionTypeKey];
+  RTCSdpType type = [[self class] typeForString:typeString];
   NSString *sdp = dictionary[kRTCSessionDescriptionSdpKey];
   return [[RTCSessionDescription alloc] initWithType:type sdp:sdp];
 }
 
 - (NSData *)JSONData {
+  NSString *type = [[self class] stringForType:self.type];
   NSDictionary *json = @{
-    kRTCSessionDescriptionTypeKey : self.type,
-    kRTCSessionDescriptionSdpKey : self.description
+    kRTCSessionDescriptionTypeKey : type,
+    kRTCSessionDescriptionSdpKey : self.sdp
   };
   return [NSJSONSerialization dataWithJSONObject:json options:0 error:nil];
 }
 
 @end