Pass around the candidate removals events in IOS clients

webrtc/examples/objc/AppRTCDemo/ARDAppClient.m

Index: webrtc/examples/objc/AppRTCDemo/ARDAppClient.m
diff --git a/webrtc/examples/objc/AppRTCDemo/ARDAppClient.m b/webrtc/examples/objc/AppRTCDemo/ARDAppClient.m
index 86d18d1333c6b1bd58f77a366e557ff062e82010..8fb1841e391a16eb814235c21abd7a4dcc781eda 100644
--- a/webrtc/examples/objc/AppRTCDemo/ARDAppClient.m
+++ b/webrtc/examples/objc/AppRTCDemo/ARDAppClient.m
@@ -330,6 +330,7 @@ static BOOL const kARDAppClientEnableTracing = NO;
       [_messageQueue insertObject:message atIndex:0];
       break;
     case kARDSignalingMessageTypeCandidate:
+    case kARDSignalingMessageTypeCandidateRemoval:
       [_messageQueue addObject:message];
       break;
     case kARDSignalingMessageTypeBye:
@@ -410,6 +411,16 @@ static BOOL const kARDAppClientEnableTracing = NO;
 }
 
 - (void)peerConnection:(RTCPeerConnection *)peerConnection
+    didRemoveIceCandidates:(NSArray<RTCIceCandidate *> *)candidates {
+  dispatch_async(dispatch_get_main_queue(), ^{
+    ARDICECandidateRemovalMessage *message =
+        [[ARDICECandidateRemovalMessage alloc]
+            initWithRemovedCandidates:candidates];
+    [self sendSignalingMessage:message];
+  });
+}
+
+- (void)peerConnection:(RTCPeerConnection *)peerConnection
     didOpenDataChannel:(RTCDataChannel *)dataChannel {
 }
 
@@ -573,6 +584,12 @@ static BOOL const kARDAppClientEnableTracing = NO;
       [_peerConnection addIceCandidate:candidateMessage.candidate];
       break;
     }
+    case kARDSignalingMessageTypeCandidateRemoval: {
+      ARDICECandidateRemovalMessage *candidateMessage =
+          (ARDICECandidateRemovalMessage *)message;
+      [_peerConnection removeIceCandidates:candidateMessage.candidates];
+      break;
+    }
     case kARDSignalingMessageTypeBye:
       // Other client disconnected.
       // TODO(tkchin): support waiting in room for next client. For now just